Event tracing requires pulling in timing counters, so we can sync
with Chromium's timestamps. It may require a bit more tricky stuff
to sync ANGLE's GPU timestamps with trace timestamps, but should
allow us to add GPU trace events in the future.

BUG=chromium:436191
BUG=angleproject:966

Change-Id: Ie1dc2981650d96888f988fa74b6fa435fbe8edc2
Reviewed-on: https://chromium-review.googlesource.com/263781Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>