A better idle time estimator

components/scheduler/renderer/idle_time_estimator.h

+// Copyright 2015 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_IDLE_TIME_ESTIMATOR_H_
+#define COMPONENTS_SCHEDULER_RENDERER_IDLE_TIME_ESTIMATOR_H_
+
+#include "base/message_loop/message_loop.h"
+#include "base/time/tick_clock.h"
+#include "cc/base/rolling_time_delta_history.h"
+#include "components/scheduler/scheduler_export.h"
+
+namespace scheduler {
+
+// Estimates how much idle time there is avaliable.

[Sami, 2015/10/09 02:32:18]

typo: available

[alex clarke (OOO till 29th), 2015/10/15 13:24:01]

Done.

+class SCHEDULER_EXPORT IdleTimeEstimator
+    : public base::MessageLoop::TaskObserver {
+ public:
+  IdleTimeEstimator(int sample_count, double estimation_percentile);

[Sami, 2015/10/09 02:32:18]

I think it would be slightly less error prone to pass in the compositor task
runner to the constructor and have this class automatically register itself as a
task observer instead of relying on the user to do remember to do that.

[alex clarke (OOO till 29th), 2015/10/15 13:24:01]

Done.

+
+  ~IdleTimeEstimator() override;
+
+  // Expected Idle time is defined as: expected frame duration minus
+  // expected compositor task duration, where the frame duration is clamped to a
+  // meximum of |max_frame_length|.

[Sami, 2015/10/09 02:32:18]

typo: maximum

[alex clarke (OOO till 29th), 2015/10/15 13:24:01]

Done.

+  base::TimeDelta GetExpectedIdleDuration(
+      base::TimeDelta max_frame_length) const;
+
+  void DidCommitFrameToCompositor();
+
+  void Clear();
+
+  // TaskObserver implementation:
+  void WillProcessTask(const base::PendingTask& pending_task) override;
+  void DidProcessTask(const base::PendingTask& pending_task) override;
+
+  void SetTimeSourceForTesting(scoped_ptr<base::TickClock> time_source);
+
+ private:
+  cc::RollingTimeDeltaHistory frame_length_;
+  cc::RollingTimeDeltaHistory per_frame_compositor_task_runtime_;
+  scoped_ptr<base::TickClock> time_source_;
+  double estimation_percentile_;
+
+  base::TimeTicks task_start_time_;
+  base::TimeTicks prev_commit_time_;
+  base::TimeDelta cumulative_compositor_runtime_;
+  bool did_commit_;
+
+  DISALLOW_COPY_AND_ASSIGN(IdleTimeEstimator);
+};
+
+}  // namespace scheduler
+
+#endif  // COMPONENTS_SCHEDULER_RENDERER_IDLE_TIME_ESTIMATOR_H_