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

third_party/WebKit/Source/platform/scheduler/base/long_task_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 THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_LONG_TASK_TRACKER_H_
-#define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_LONG_TASK_TRACKER_H_
-
-#include <vector>
-
-#include "base/macros.h"
-#include "base/time/time.h"
-#include "public/platform/WebCommon.h"
-
-namespace blink {
-namespace scheduler {
-
-// Records and reports long task times, above the threshold.
-// The threshold is set to 50ms in the implementation.
-class BLINK_PLATFORM_EXPORT LongTaskTracker {
- public:
-  using LongTaskTiming =
-      std::vector<std::pair<base::TimeTicks, base::TimeDelta>>;
-
-  LongTaskTracker();
-  ~LongTaskTracker();
-
-  LongTaskTiming GetLongTaskTiming();
-  void RecordLongTask(base::TimeTicks startTime, base::TimeDelta duration);
-
- private:
-  friend class LongTaskTrackerTest;
-
-  LongTaskTiming long_task_times_;
-
-  DISALLOW_COPY_AND_ASSIGN(LongTaskTracker);
-};
-
-}  // namespace scheduler
-}  // namespace blink
-
-#endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_LONG_TASK_TRACKER_H_