Implement the "messageevent" argument to Document#createEvent. #4008

[johnathan79717]

This is a fix for issue #4008.

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/3397

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[jdm]

r+

[johnathan79717]

Thanks a lot!!!

[bors-servo]

saw approval from jdm
at johnathan79717@ccb4e8b

[bors-servo]

merging johnathan79717/servo/4008 = ccb4e8b into auto

[bors-servo]

johnathan79717/servo/4008 = ccb4e8b merged ok, testing candidate = bd92c88

[bors-servo]

some tests failed:
failure: http://build.servo.org/builders/linux2/builds/183
failure: http://build.servo.org/builders/mac1/builds/400

[jdm]

/dom/events/EventTarget-dispatchEvent.html
------------------------------------------
PASS expected FAIL If the event's initialized flag is not set, an InvalidStateError must be thrown (MessageEvent).

This will need to remove this expected failure from tests/wpt/metadata/dom/events/EventTarget-dispatchEvent.html.ini.

[johnathan79717]

@jdm
I have removed the expected failure as you suggested, thanks.

[Manishearth]

r=jdm

[bors-servo]

saw approval from jdm
at johnathan79717@8b8eea1

[bors-servo]

merging johnathan79717/servo/4008 = 8b8eea1 into auto

[bors-servo]

johnathan79717/servo/4008 = 8b8eea1 merged ok, testing candidate = bdb3a25

[bors-servo]

all tests pass:
success: http://build.servo.org/builders/linux1/builds/199
success: http://build.servo.org/builders/linux2/builds/199
success: http://build.servo.org/builders/android/builds/266
success: http://build.servo.org/builders/mac1/builds/416
success: http://build.servo.org/builders/mac2/builds/416

[bors-servo]

fast-forwarding master to auto = bdb3a25