All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=838453

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=c7bf58ef1e350f3b6df37b1f45a9ce73e2c4425538b16d9f256685eed0fb0cd3


Bot(s) for this bug's original alert(s):

linux
mac

Assigning to oysteine@chromium.org because this is the only CL in range:
Perfetto: Trace Event layer

This adds alternate implementations of the TraceEventAgent and Coordinator Mojo classes
in the tracing service, which uses Perfetto rather than the TraceLog behind the scenes.

It's enabled using --enable-features=TracingPerfettoBackend.

This also renames the ChromeTraceEventAgent to TraceEventAgent,
as it's not actually "Chrome" specific.

Change-Id: I377c8613e5c4a6d593d5ae1ab6f102bd3e6720cc
Reviewed-on: https://chromium-review.googlesource.com/981270
Commit-Queue: oysteine <oysteine@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Primiano Tucci <primiano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554090}