cc: Add back a benchmark category trace for counting renderer frames

tools/perf/metrics/timeline.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 import collections
 
 from telemetry.util.statistics import DivideIfPossibleOrZero
 from telemetry.value import scalar
 from telemetry.web_perf.metrics import timeline_based_metric
 
 
@@ skipping 82 matching lines @@
 NoThreads = []
 FastPathThreads = ["GPU", "renderer_compositor", "browser", "IO"]
 
 ReportMainThreadOnly = ["renderer_main"]
 ReportSilkDetails = ["renderer_main"]
 
 # TODO(epenner): Thread names above are likely fairly stable but trace names
 # could change. We should formalize these traces to keep this robust.
 OverheadTraceCategory = "trace_event_overhead"
 OverheadTraceName = "overhead"
-FrameTraceName = "::SwapBuffers"
+FrameTraceName = "::DrawLayers"

[danakj, 2016/10/20 22:25:43]

Should this be LayerTreeHostImpl::DrawLayers maybe? That'd be extra trace-able.
I'll do that.

 FrameTraceThreadName = "renderer_compositor"
 
 IntervalNames = ["frame", "second"]
 
 
 def Rate(numerator, denominator):
   return DivideIfPossibleOrZero(numerator, denominator)
 
 
 def ClockOverheadForEvent(event):
@@ skipping 201 matching lines @@
           thread_results.AddDetailedResults(
               num_intervals, interval_name, results)
 
     # Report mean frame time for the frame rate thread. We could report other
     # frame rates (e.g. renderer_main) but this might get confusing.
     mean_frame_time = Rate(frame_rate_thread.all_action_time, num_frames)
     results.AddValue(scalar.ScalarValue(
         results.current_page,
         ThreadMeanFrameTimeResultName(FrameTraceThreadName),
         "ms", mean_frame_time))