There are now fewer failures.  One category involves the failure of Blink bindings to properly name interface prototype objects, and I am filing a separate issue for that.

assert_equals: class string of Presentation.prototype expected "[object PresentationPrototype]" but got "[object Presentation]"
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1002:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:906:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
Pass	Presentation interface: existence and properties of interface prototype object's "constructor" property	
Pass	Presentation interface: attribute defaultRequest	
Pass	Presentation must be primary interface of navigator.presentation	
Pass	Stringification of navigator.presentation	
Pass	Presentation interface: navigator.presentation must inherit property "defaultRequest" with the proper type (0)	
Pass	PresentationRequest interface: existence and properties of interface object	
Pass	PresentationRequest interface object length	
Pass	PresentationRequest interface object name	
Fail	PresentationRequest interface: existence and properties of interface prototype object	assert_equals: class string of PresentationRequest.prototype expected "[object PresentationRequestPrototype]" but got "[object PresentationRequest]"
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1002:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:906:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
Pass	PresentationRequest interface: existence and properties of interface prototype object's "constructor" property	
Fail	PresentationRequest interface: operation start()	assert_unreached: Throws "TypeError: Illegal invocation" instead of rejecting promise Reached unreachable code
    at Object.<anonymous> (http://localhost:8000/resources/idlharness.js:83:17)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at throwOrReject (http://localhost:8000/resources/idlharness.js:82:20)
    at IdlObject.IdlInterface.do_member_operation_asserts (http://localhost:8000/resources/idlharness.js:1292:13)
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1235:14)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
Fail	PresentationRequest interface: operation reconnect(DOMString)	assert_unreached: Throws "TypeError: Illegal invocation" instead of rejecting promise Reached unreachable code
    at Object.<anonymous> (http://localhost:8000/resources/idlharness.js:83:17)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at throwOrReject (http://localhost:8000/resources/idlharness.js:82:20)
    at IdlObject.IdlInterface.do_member_operation_asserts (http://localhost:8000/resources/idlharness.js:1292:13)
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1235:14)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
Fail	PresentationRequest interface: operation getAvailability()	assert_unreached: Throws "TypeError: Illegal invocation" instead of rejecting promise Reached unreachable code
    at Object.<anonymous> (http://localhost:8000/resources/idlharness.js:83:17)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at throwOrReject (http://localhost:8000/resources/idlharness.js:82:20)
    at IdlObject.IdlInterface.do_member_operation_asserts (http://localhost:8000/resources/idlharness.js:1292:13)
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1235:14)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
Pass	PresentationRequest interface: attribute onconnectionavailable	
Fail	Stringification of navigator.presentation.defaultRequest	assert_equals: class string of navigator.presentation.defaultRequest expected "[object PresentationRequest]" but got "[object Null]"
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1494:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_primary_interface_of (http://localhost:8000/resources/idlharness.js:1490:5)
    at IdlObject.IdlInterface.test_object (http://localhost:8000/resources/idlharness.js:1440:10)
Fail	PresentationRequest interface: navigator.presentation.defaultRequest must inherit property "start" with the proper type (0)	Cannot use 'in' operator to search for 'hasOwnProperty' in null
TypeError: Cannot use 'in' operator to search for 'hasOwnProperty' in null
    at http://localhost:8000/resources/testharness.js:1134:37
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1546:25)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_interface_of (http://localhost:8000/resources/idlharness.js:1540:13)
    at IdlObject.IdlInterface.test_object (http://localhost:8000/resources/idlharness.js:1452:27)
    at .<anonymous> (http://localhost:8000/resources/idlharness.js:403:36)
    at Array.forEach (native)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:401:32)
    at http://localhost:8000/presentation-api/controlling-ua/idlharness.html:121:19
Fail	PresentationRequest interface: navigator.presentation.defaultRequest must inherit property "reconnect" with the proper type (1)	Cannot use 'in' operator to search for 'hasOwnProperty' in null
TypeError: Cannot use 'in' operator to search for 'hasOwnProperty' in null
    at http://localhost:8000/resources/testharness.js:1134:37
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1546:25)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_interface_of (http://localhost:8000/resources/idlharness.js:1540:13)
    at IdlObject.IdlInterface.test_object (http://localhost:8000/resources/idlharness.js:1452:27)
    at .<anonymous> (http://localhost:8000/resources/idlharness.js:403:36)
    at Array.forEach (native)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:401:32)
    at http://localhost:8000/presentation-api/controlling-ua/idlharness.html:121:19
Fail	PresentationRequest interface: calling reconnect(DOMString) on navigator.presentation.defaultRequest with too few arguments must throw TypeError	Cannot use 'in' operator to search for 'hasOwnProperty' in null
TypeError: Cannot use 'in' operator to search for 'hasOwnProperty' in null
    at http://localhost:8000/resources/testharness.js:1134:37
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1595:25)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at IdlObject.IdlInterface.test_interface_of (http://localhost:8000/resources/idlharness.js:1589:20)
    at IdlObject.IdlInterface.test_object (http://localhost:8000/resources/idlharness.js:1452:27)
    at .<anonymous> (http://localhost:8000/resources/idlharness.js:403:36)
    at Array.forEach (native)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:401:32)
    at http://localhost:8000/presentation-api/controlling-ua/idlharness.html:121:19
    at http://localhost:8000/presentation-api/controlling-ua/idlharness.html:122:7
Fail	PresentationRequest interface: navigator.presentation.defaultRequest must inherit property "getAvailability" with the proper type (2)	Cannot use 'in' operator to search for 'hasOwnProperty' in null
TypeError: Cannot use 'in' operator to search for 'hasOwnProperty' in null
    at http://localhost:8000/resources/testharness.js:1134:37
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1546:25)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_interface_of (http://localhost:8000/resources/idlharness.js:1540:13)
    at IdlObject.IdlInterface.test_object (http://localhost:8000/resources/idlharness.js:1452:27)
    at .<anonymous> (http://localhost:8000/resources/idlharness.js:403:36)
    at Array.forEach (native)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:401:32)
    at http://localhost:8000/presentation-api/controlling-ua/idlharness.html:121:19
Fail	PresentationRequest interface: navigator.presentation.defaultRequest must inherit property "onconnectionavailable" with the proper type (3)	Cannot use 'in' operator to search for 'hasOwnProperty' in null
TypeError: Cannot use 'in' operator to search for 'hasOwnProperty' in null
    at http://localhost:8000/resources/testharness.js:1134:37
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1546:25)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_interface_of (http://localhost:8000/resources/idlharness.js:1540:13)
    at IdlObject.IdlInterface.test_object (http://localhost:8000/resources/idlharness.js:1452:27)
    at .<anonymous> (http://localhost:8000/resources/idlharness.js:403:36)
    at Array.forEach (native)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:401:32)
    at http://localhost:8000/presentation-api/controlling-ua/idlharness.html:121:19
Pass	PresentationRequest must be primary interface of new PresentationRequest("/presentation-api/receiving-ua/idlharness.html")	
Pass	Stringification of new PresentationRequest("/presentation-api/receiving-ua/idlharness.html")	
Pass	PresentationRequest interface: new PresentationRequest("/presentation-api/receiving-ua/idlharness.html") must inherit property "start" with the proper type (0)	
Pass	PresentationRequest interface: new PresentationRequest("/presentation-api/receiving-ua/idlharness.html") must inherit property "reconnect" with the proper type (1)	
Pass	PresentationRequest interface: calling reconnect(DOMString) on new PresentationRequest("/presentation-api/receiving-ua/idlharness.html") with too few arguments must throw TypeError	
Pass	PresentationRequest interface: new PresentationRequest("/presentation-api/receiving-ua/idlharness.html") must inherit property "getAvailability" with the proper type (2)	
Pass	PresentationRequest interface: new PresentationRequest("/presentation-api/receiving-ua/idlharness.html") must inherit property "onconnectionavailable" with the proper type (3)	
Pass	PresentationAvailability interface: existence and properties of interface object	
Pass	PresentationAvailability interface object length	
Pass	PresentationAvailability interface object name	
Fail	PresentationAvailability interface: existence and properties of interface prototype object	assert_equals: class string of PresentationAvailability.prototype expected "[object PresentationAvailabilityPrototype]" but got "[object PresentationAvailability]"
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1002:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:906:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
Pass	PresentationAvailability interface: existence and properties of interface prototype object's "constructor" property	
Pass	PresentationAvailability interface: attribute value	
Pass	PresentationAvailability interface: attribute onchange	
Pass	PresentationConnectionAvailableEvent interface: existence and properties of interface object	
Pass	PresentationConnectionAvailableEvent interface object length	
Pass	PresentationConnectionAvailableEvent interface object name	
Fail	PresentationConnectionAvailableEvent interface: existence and properties of interface prototype object	assert_equals: class string of PresentationConnectionAvailableEvent.prototype expected "[object PresentationConnectionAvailableEventPrototype]" but got "[object PresentationConnectionAvailableEvent]"
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1002:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:906:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
Pass	PresentationConnectionAvailableEvent interface: existence and properties of interface prototype object's "constructor" property	
Pass	PresentationConnectionAvailableEvent interface: attribute connection	
Pass	PresentationConnection interface: existence and properties of interface object	
Pass	PresentationConnection interface object length	
Pass	PresentationConnection interface object name	
Fail	PresentationConnection interface: existence and properties of interface prototype object	assert_equals: class string of PresentationConnection.prototype expected "[object PresentationConnectionPrototype]" but got "[object PresentationConnection]"
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1002:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:906:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
Pass	PresentationConnection interface: existence and properties of interface prototype object's "constructor" property	
Pass	PresentationConnection interface: attribute id	
Pass	PresentationConnection interface: attribute state	
Pass	PresentationConnection interface: operation close()	
Pass	PresentationConnection interface: operation terminate()	
Pass	PresentationConnection interface: attribute onconnect	
Pass	PresentationConnection interface: attribute onclose	
Pass	PresentationConnection interface: attribute onterminate	
Pass	PresentationConnection interface: attribute binaryType	
Pass	PresentationConnection interface: attribute onmessage	
Pass	PresentationConnection interface: operation send(DOMString)	
Pass	PresentationConnection interface: operation send(Blob)	
Pass	PresentationConnection interface: operation send(ArrayBuffer)	
Pass	PresentationConnection interface: operation send(ArrayBufferView)	
Fail	PresentationConnectionClosedEvent interface: existence and properties of interface object	assert_own_property: self does not have own property "PresentationConnectionClosedEvent" expected property "PresentationConnectionClosedEvent" missing
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:767:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:747:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:398:28)
Fail	PresentationConnectionClosedEvent interface object length	assert_own_property: self does not have own property "PresentationConnectionClosedEvent" expected property "PresentationConnectionClosedEvent" missing
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:858:13)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:854:9)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:398:28)
Fail	PresentationConnectionClosedEvent interface object name	assert_own_property: self does not have own property "PresentationConnectionClosedEvent" expected property "PresentationConnectionClosedEvent" missing
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:885:13)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:881:9)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:398:28)
Fail	PresentationConnectionClosedEvent interface: existence and properties of interface prototype object	assert_own_property: self does not have own property "PresentationConnectionClosedEvent" expected property "PresentationConnectionClosedEvent" missing
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:915:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:906:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:398:28)
Fail	PresentationConnectionClosedEvent interface: existence and properties of interface prototype object's "constructor" property	assert_own_property: self does not have own property "PresentationConnectionClosedEvent" expected property "PresentationConnectionClosedEvent" missing
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1018:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_self (http://localhost:8000/resources/idlharness.js:1012:5)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:731:14)
    at IdlArray.test (http://localhost:8000/resources/idlharness.js:398:28)
Fail	PresentationConnectionClosedEvent interface: attribute reason	assert_own_property: self does not have own property "PresentationConnectionClosedEvent" expected property "PresentationConnectionClosedEvent" missing
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1119:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_member_attribute (http://localhost:8000/resources/idlharness.js:1113:5)
    at IdlObject.IdlInterface.test_members (http://localhost:8000/resources/idlharness.js:1395:22)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:740:10)
Fail	PresentationConnectionClosedEvent interface: attribute message	assert_own_property: self does not have own property "PresentationConnectionClosedEvent" expected property "PresentationConnectionClosedEvent" missing
    at IdlObject.<anonymous> (http://localhost:8000/resources/idlharness.js:1119:9)
    at Object.Test.step (http://localhost:8000/resources/testharness.js:1403:25)
    at test (http://localhost:8000/resources/testharness.js:501:18)
    at IdlObject.IdlInterface.test_member_attribute (http://localhost:8000/resources/idlharness.js:1113:5)
    at IdlObject.IdlInterface.test_members (http://localhost:8000/resources/idlharness.js:1395:22)
    at IdlObject.IdlInterface.test (http://localhost:8000/resources/idlharness.js:740:10)

[Note: I'm looking at cleaning these up in preparation for landing a patch for multiple URLs per PresentationRequest.]

Category #3 of failures is because the idl harness is trying to test navigator.presentation.defaultRequest without setting it first, so all the tests fail against |null|.  Will file an upstream bug against idlharness.

Filed https://github.com/w3c/presentation-api/issues/324 and https://github.com/w3c/web-platform-tests/issues/3294 for the next two categories of failures.

All of the failures noted today are blocked by bugs in the bindings, the tests, or the spec itself.  Unassigning until progress is made on those.

#10 "idl harness is trying to test navigator.presentation.defaultRequest without setting it first, so all the tests fail against |null|" isn't this the same as  Issue 627309  (which you duped against)? From my reading, this is not an upstream bug in idlharness, but a bug in Chrome's bindings generator.

navigator.presentation.defaultRequest is an attribute default to null, not a function, so I think it's a separate issue.  The harness is trying to enumerate the properties of |null| and failing.

https://github.com/w3c/web-platform-tests/pull/3533 fixes defaultRequest.

This seems to work now :)

There's still a failure in the wpt.fyi dashboard that we should investigate.

http://wpt.fyi/presentation-api/controlling-ua

Just to clarify, the bug was opened about the idlharness.html test (ie. WebIDL tests). We might want to rename the bug or file a new one?

Good point, the WebIDL tests are all passing now.  Should file a separate bug if there are reproducible failures in other WPT.