Add PerformanceObserver.supportedEntryTypes

Blink intent:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/XZU_DhQ9ZGs

Bug: 911314
Change-Id: I4a79d6d3a81ec260c7db5c2bea7b2d533a1285b2
Reviewed-on: https://chromium-review.googlesource.com/c/1359480
Reviewed-by: Yoav Weiss <yoav@yoav.ws>
Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615924}
24 files changed