GitLab

This CL adds a UseCounter that tracks the two ways to use EventTiming
explicitly:
* getEntriesByType or getEntriesByName with event/firstInput.
* Having PerformanceObservers of event/firstInput.

Bug: 851484
Change-Id: I8c2af71d089dbbf7db87b94b8b5d9f56e1699998
Reviewed-on: https://chromium-review.googlesource.com/1115511Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570539}