Report expected task queueing time via UMA

components/scheduler/base/queueing_time_estimator.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 COMPONENTS_SCHEDULER_RENDERER_QUEUEING_TIME_ESTIMATOR_H_
+#define COMPONENTS_SCHEDULER_RENDERER_QUEUEING_TIME_ESTIMATOR_H_
+
+#include "base/macros.h"
+#include "base/message_loop/message_loop.h"
+#include "base/time/time.h"
+#include "components/scheduler/scheduler_export.h"
+
+namespace base {
+class TickClock;
+}
+
+namespace scheduler {
+
+// Records the expected queueing time for a high priority task occurring
+// randomly during each interval of length |window_duration|.
+class SCHEDULER_EXPORT QueueingTimeEstimator {
+ public:
+  class SCHEDULER_EXPORT Client {
+   public:
+    virtual void OnQueueingTimeForWindowEstimated(
+        base::TimeDelta queueing_time) = 0;
+    Client() {}
+    virtual ~Client() {}
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(Client);
+  };
+
+  QueueingTimeEstimator(Client* client,
+                        base::TimeDelta window_duration);
+
+  void OnToplevelTaskCompleted(base::TimeTicks task_start_time,
+                               base::TimeTicks task_end_time);
+
+ private:
+  bool TimePastWindowEnd(base::TimeTicks task_end_time);
+  Client* client_;  // NOT OWNED.
+
+  base::TimeDelta current_expected_queueing_time_;
+  base::TimeDelta window_duration_;
+  base::TimeTicks window_start_time_;
+
+  DISALLOW_COPY_AND_ASSIGN(QueueingTimeEstimator);
+};
+
+}  // namespace scheduler
+
+#endif  // COMPONENTS_SCHEDULER_RENDERER_QUEUEING_TIME_ESTIMATOR_H_