Report the duration of sampled tasks with histogram.

components/scheduler/renderer/renderer_task_duration.h

Index: components/scheduler/renderer/renderer_task_duration.h
diff --git a/components/scheduler/renderer/renderer_task_duration.h b/components/scheduler/renderer/renderer_task_duration.h
new file mode 100644
index 0000000000000000000000000000000000000000..0fae8700de35c236796eea917af18e6f431f0383
--- /dev/null
+++ b/components/scheduler/renderer/renderer_task_duration.h
@@ -0,0 +1,22 @@
+// Copyright 2016 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.
+
+#ifndef COMPONENTS_SCHEDULER_RENDERER_RENDERER_TASK_DURATION_H_
+#define COMPONENTS_SCHEDULER_RENDERER_RENDERER_TASK_DURATION_H_
+
+#include "base/time/time.h"
+
+namespace scheduler {
+class RendererTaskDuration {

[majidvp, 2016/07/27 13:50:59]

I think the convention is to have a blank line before class declaration but I
couldn't find it in
the style guide. So I am fine either way.

[majidvp, 2016/07/27 13:50:59]

I think a better name may be a TaskDurationReporter.
Also please add a class comment explaining what this class does and
in particular the sampling interval.

[sunyunjia, 2016/07/27 17:28:42]

Done.

[sunyunjia, 2016/07/27 17:28:42]

Done.

+ public:
+  RendererTaskDuration();
+  ~RendererTaskDuration();
+  void ReportSampleDuration(base::TimeDelta duration);
+  static const int kSampleInterval = 100;

[majidvp, 2016/07/27 13:50:59]

This constant does not need to be public. Please move to the implementation
file.

[sunyunjia, 2016/07/27 17:28:43]

Done.

+ private:
+  int sample_count_;
+};

[majidvp, 2016/07/27 13:50:59]

This class is not meant to be copies/moved so please prevent these by using
DISALLOW_COPY_AND_ASSIGN macro. 

[sunyunjia, 2016/07/27 17:28:42]

Done.

+}
+
+#endif // COMPONENTS_SCHEDULER_RENDERER_RENDERER_TASK_DURATION_H_