Delivering the FIRST_NONEMPTY_PAINT phase changing event to base/

components/metrics/profiler/tracking_synchronizer_observer.h

Index: components/metrics/profiler/tracking_synchronizer_observer.h
diff --git a/components/metrics/profiler/tracking_synchronizer_observer.h b/components/metrics/profiler/tracking_synchronizer_observer.h
index 0e943508079bd814169fae18b759ff563f74c21f..f880a78209373b9597103ee737b72b9c3a25cf82 100644
--- a/components/metrics/profiler/tracking_synchronizer_observer.h
+++ b/components/metrics/profiler/tracking_synchronizer_observer.h
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "base/process/process_handle.h"
+#include "base/time/time.h"
 #include "components/metrics/proto/chrome_user_metrics_extension.pb.h"
 #include "content/public/common/process_type.h"
 
@@ -29,19 +30,14 @@ typedef std::vector<ProfilerEventProto::ProfilerEvent> ProfilerEvents;
 // Observer for notifications from the TrackingSynchronizer class.
 class TrackingSynchronizerObserver {
  public:
-  // TODO(vadimt): Consider isherman@ idea: I'd change the phase_start and
-  // phase_finish from TimeDeltas to TimeTicks.  And I'd omit the |past_events|
-  // list -- either in favor of a single ProfilerEvent that corresponds to the
-  // phase, or a method on the TrackingSynchronizer that can translate a
-  // profiling_phase to a ProfilerEvent.
-
   // Received |process_data_phase| for profiling phase |profiling_phase| from a
-  // single process of |process_type|. The phase start and finish times,
-  // relative to the start time are |phase_start| and
-  // |phase_finish|. All profiling phases prior to the reported one have already
-  // completed, and each completion was associated with an instance of
-  // ProfilerEventProto::ProfilerEvent. |past_events| contains events associated
-  // with completions of phases prior to the reported one.
+  // single process of |process_type|. The phase start and finish times are
+  // |phase_start| and |phase_finish|.
+  // Each completed phase is associated with an event that triggered the
+  // completion of the phase. |past_events| contains the set of events that
+  // completed prior to the reported phase. This data structure is useful for
+  // quickly computing the full set of profiled traces that occurred before or
+  // after a given event.
   // The observer should assume there might be more data coming until
   // FinishedReceivingData() is called.
   virtual void ReceivedProfilerData(
@@ -49,8 +45,8 @@ class TrackingSynchronizerObserver {
       base::ProcessId process_id,
       content::ProcessType process_type,
       int profiling_phase,
-      base::TimeDelta phase_start,
-      base::TimeDelta phase_finish,
+      base::TimeTicks phase_start,
+      base::TimeTicks phase_finish,
       const ProfilerEvents& past_events) = 0;
 
   // The observer should not expect any more calls to |ReceivedProfilerData()|