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/base/task_queue.h"
+#include "components/scheduler/scheduler_export.h"
+
+namespace scheduler {
+
+// Estimates how much idle time there is available.
+class SCHEDULER_EXPORT IdleTimeEstimator
+    : public base::MessageLoop::TaskObserver {
+ public:
+  IdleTimeEstimator(const scoped_refptr<TaskQueue>& compositor_task_runner,
+                    int sample_count,
+                    double estimation_percentile);
+
+  ~IdleTimeEstimator() override;
+
+  // Expected Idle time is defined as: |compositor_frame_interval| minus
+  // expected compositor task duration.
+  base::TimeDelta GetExpectedIdleDuration(
+      base::TimeDelta compositor_frame_interval) 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:
+  scoped_refptr<TaskQueue> compositor_task_runner_;
+  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_;
+  int nesting_level_;
+  bool did_commit_;
+
+  DISALLOW_COPY_AND_ASSIGN(IdleTimeEstimator);
+};
+
+}  // namespace scheduler
+
+#endif  // COMPONENTS_SCHEDULER_RENDERER_IDLE_TIME_ESTIMATOR_H_