[EventTiming] Make PerformanceEventTiming Exposed=Window

This CL makes PerformanceEventTiming IDL consistent with the spec, after
https://github.com/WICG/event-timing/pull/16. Note that EventCount is
not yet implemented.

Bug: 823744
Change-Id: I01779ed82cba0cfea0542ab74cc95b4e7adc8aac
Reviewed-on: https://chromium-review.googlesource.com/c/1363961
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614360}
1 file changed