Report expected task queueing time via UMA

components/scheduler/base/task_time_tracker.h

+// 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 CONTENT_RENDERER_SCHEDULER_BASE_TASK_TIME_TRACKER_H_
+#define CONTENT_RENDERER_SCHEDULER_BASE_TASK_TIME_TRACKER_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/time/default_tick_clock.h"
+#include "base/time/time.h"
+#include "components/scheduler/base/queueing_time_estimator.h"
+#include "components/scheduler/scheduler_export.h"
+
+namespace scheduler {
+
+class SCHEDULER_EXPORT TaskTimeTracker {

[Sami, 2016/07/06 10:08:29]

Is there a reason to keep TaskTimeTracker and TaskTimeTracker::Observer
separate? I was thinking we could merge them into a pure virtual
TaskTimeObserver that only has ReportTaskTime in it. WDYT?

[tdresser, 2016/07/06 13:25:34]

Done.

+ public:
+  class SCHEDULER_EXPORT Observer {

[alex clarke (OOO till 29th), 2016/07/06 09:51:39]

Nit:  DISALLOW_COPY_AND_ASSIGN(Observer)

[tdresser, 2016/07/06 13:25:34]

No longer needed.

+   public:
+    virtual void ReportTaskTime(base::TimeTicks start_time,
+                                base::TimeTicks end_time) = 0;
+    virtual ~Observer() {}
+  };
+
+  TaskTimeTracker(Observer* observer);

[alex clarke (OOO till 29th), 2016/07/06 09:51:39]

nit: explicit

[tdresser, 2016/07/06 13:25:34]

No longer needed.

+  ~TaskTimeTracker();
+
+  void ReportTaskTime(base::TimeTicks startTime, base::TimeTicks endTime);
+
+ private:
+  // Not owned.
+  Observer* observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskTimeTracker);
+};
+
+} // namespace scheduler
+
+#endif // CONTENT_RENDERER_SCHEDULER_BASE_TASK_TIME_TRACKER_H_