Report the duration of sampled tasks with histogram.

components/scheduler/renderer/renderer_scheduler_impl.h

Index: components/scheduler/renderer/renderer_scheduler_impl.h
diff --git a/components/scheduler/renderer/renderer_scheduler_impl.h b/components/scheduler/renderer/renderer_scheduler_impl.h
index d662dd45247bfbc44717b04897dc22e3ae2eed74..d38affc668d4123ba4b0c7e67698df550cd7a3d8 100644
--- a/components/scheduler/renderer/renderer_scheduler_impl.h
+++ b/components/scheduler/renderer/renderer_scheduler_impl.h
@@ -19,6 +19,7 @@
 #include "components/scheduler/renderer/render_widget_signals.h"
 #include "components/scheduler/renderer/renderer_scheduler.h"
 #include "components/scheduler/renderer/task_cost_estimator.h"
+#include "components/scheduler/renderer/task_duration_reporter.h"
 #include "components/scheduler/renderer/throttling_helper.h"
 #include "components/scheduler/renderer/user_model.h"
 #include "components/scheduler/renderer/web_view_scheduler_impl.h"
@@ -470,6 +471,9 @@ class SCHEDULER_EXPORT RendererSchedulerImpl
   }
 
   PollableThreadSafeFlag policy_may_need_update_;
+
+  TaskDurationReporter duration_reporter_;

[tdresser, 2016/07/27 18:04:25]

I think we can put this in MainThreadOnly(), to make it clear what thread this
is accessed from.

[sunyunjia, 2016/07/27 19:51:04]

Done.

+
   base::WeakPtrFactory<RendererSchedulerImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererSchedulerImpl);