Chrome Version: 58.0.2991.0
OS: macOS 10.12.2

What steps will reproduce the problem?
(1) Open http://w3c-test.org/dom/events/EventTarget-dispatchEvent.html in Chrome.
(2) Observe the test results.

What is the expected result?
All the tests should pass.

What happens instead?
Three tests fail:
Fail    If the event's initialized flag is not set, an InvalidStateError must be thrown (BeforeUnloadEvent).
    assert_equals: Event type should be empty string before initialization expected "" but got "beforeunload"
Fail    If the event's initialized flag is not set, an InvalidStateError must be thrown (CloseEvent).
   assert_equals: Event type should be empty string before initialization expected "" but got "close"
Fail    If the event's initialized flag is not set, an InvalidStateError must be thrown (PopStateEvent).
    assert_equals: Event type should be empty string before initialization expected "" but got "popstate"

Further details:
These tests contain the equivalent of:
    assertEquals(document.createEvent(someEventInterfaceName).type, "")
where someEventInterfaceName is one of:
    "BeforeUnloadEvent", "CloseEvent", "PopStateEvent"

And they fail since the .type property's actual value in Chrome is, respectively:
BeforeUnloadEvent: "beforeunload"
CloseEvent:        "close"
PopStateEvent:     "popstate"

However, per step 6 of https://dom.spec.whatwg.org/#dom-document-createevent ,
the event returned from createEvent() should have its .type property set to the empty string.