Move and rename TaskTimeTracker to public interface exposed to WebThread, use in WebPerf Agent.

third_party/WebKit/public/platform/scheduler/base/task_time_observer.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 THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_TIME_OBSERVER_H_
+#define THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_TIME_OBSERVER_H_
+
+#include "base/time/time.h"
+#include "public/platform/WebCommon.h"
+
+namespace blink {
+namespace scheduler {
+
+class BLINK_PLATFORM_EXPORT TaskTimeObserver {
+ public:
+  TaskTimeObserver() {}

[alph, 2016/08/29 18:50:18]

nit: WK style on new files?

+  virtual ~TaskTimeObserver() {}
+
+  virtual void ReportTaskTime(double startTime, double endTime) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TaskTimeObserver);
+};
+
+}  // namespace scheduler
+}  // namespace blink
+
+#endif  // THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_BASE_TASK_TIME_OBSERVER_H_