CC: Add 'cc-benchmark' traces for minimal tracing in benchmarks.

tools/perf/metrics/timeline.py

Index: tools/perf/metrics/timeline.py
diff --git a/tools/perf/metrics/timeline.py b/tools/perf/metrics/timeline.py
index 3442cab15b01b00604f22a2541f4df74825a0c7f..0b1bc4281a1954bd007cdd44297a6ba741b35438 100644
--- a/tools/perf/metrics/timeline.py
+++ b/tools/perf/metrics/timeline.py
@@ -11,6 +11,18 @@ from telemetry.page import page_measurement
 TRACING_MODE = 'tracing-mode'
 TIMELINE_MODE = 'timeline-mode'
 
+# All tracing categories not disabled-by-default
+DEFAULT_TRACE_CATEGORIES = None
+
+# Categories for absolute minimum overhead tracing. This contains no
+# sub-traces of thread tasks, so it's only useful for capturing the
+# cpu-time spent on threads (as well as needed benchmark traces)
+MINIMAL_TRACE_CATEGORIES = ("toplevel,"
+                            "benchmark,"
+                            "cc-benchmark,"
+                            "webkit.console,"
+                            "trace_event_overhead")
+
 
 class MissingFramesError(page_measurement.MeasurementFailure):
   def __init__(self):
@@ -24,6 +36,7 @@ class TimelineMetric(Metric):
     """
     super(TimelineMetric, self).__init__()
     assert mode in (TRACING_MODE, TIMELINE_MODE)
+    self.trace_categories = DEFAULT_TRACE_CATEGORIES
     self._mode = mode
     self._model = None
     self._renderer_process = None
@@ -39,7 +52,7 @@ class TimelineMetric(Metric):
     if self._mode == TRACING_MODE:
       if not tab.browser.supports_tracing:
         raise Exception('Not supported')
-      tab.browser.StartTracing()
+      tab.browser.StartTracing(self.trace_categories)
     else:
       assert self._mode == TIMELINE_MODE
       tab.StartTimelineRecording()
@@ -283,6 +296,7 @@ class ThreadTimesTimelineMetric(TimelineMetric):
     super(ThreadTimesTimelineMetric, self).__init__(TRACING_MODE)
     self.results_to_report = AllThreads
     self.details_to_report = NoThreads
+    self.trace_categories = MINIMAL_TRACE_CATEGORIES
 
   def CountSlices(self, slices, substring):
     count = 0