Version: 53.0.2785.8 unknown (64-bit)
OS: Linux

What steps will reproduce the problem?
(1) Check out and setup W3C Web platform tests here:
https://github.com/w3c/web-platform-tests
(2) Run the test presentation-api/idlharness.html

What is the expected output?
ALl tests pass

What do you see instead?
Failures like the following:

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)


*******

It appears that the generated blink bindings from e.g. PresentationRequest.idl are not setting the name of the interface prototype object per the WebIDL specification [1].  e.g.

> PresentationRequest.prototype.toString() => "[object PresentationRequest]"

instead of "[object PresentationRequestPrototype]". 

This is causing these tests to fail.  I looked at the blink extended attributes for WebIDL and did not see any way to customize this property of the interface prototype object.  Perhaps I missed something?

[1] https://heycam.github.io/webidl/#interface-prototype-object (last sentence of 4.6.3)

Note this is causing failures in other test suites that use idlharness, such as gamepad, webstorage, etc. 
 
Perhaps I'm missing some IDL annotation? Philip, I believe you've done some IDL maintenance in the past?