Prevent multiple pending UpdatePolicy tasks.

content/renderer/scheduler/deadline_task_runner.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 CONTENT_RENDERER_SCHEDULER_DEADLINE_TASK_RUNNER_H_
+#define CONTENT_RENDERER_SCHEDULER_DEADLINE_TASK_RUNNER_H_
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/single_thread_task_runner.h"
+#include "base/time/time.h"
+#include "content/renderer/scheduler/cancelable_closure_holder.h"
+
+namespace content {
+
+// Runs a posted task at latest by a given deadline, but possibly sooner.
+class DeadlineTaskRunner {

[rmcilroy, 2015/03/12 22:11:30]

looks like you will need to add CONTENT_EXPORT for component builds of the tests

[alex clarke (OOO till 29th), 2015/03/13 09:53:03]

Done.

+ public:
+  DeadlineTaskRunner(const base::Closure& callback,
+                     scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+
+  ~DeadlineTaskRunner();
+
+  // If there is no outstanding task then a task is posted to run after |delay|.
+  // If there is an outstanding task which is scheduled to run:
+  //   a) sooner - then this is a NOP.
+  //   b) later - then the outstanding task is cancelled and a new task is
+  //              posted to run after |delay|.
+  //
+  // Once the deadline task has run, we reset.
+  void SetDeadline(const tracked_objects::Location& from_here,
+                   base::TimeDelta delay,
+                   base::TimeTicks now);
+
+ private:
+  void RunInternal();
+
+  CancelableClosureHolder cancelable_run_internal_;
+  base::Closure callback_;
+  base::TimeTicks deadline_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeadlineTaskRunner);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_SCHEDULER_DEADLINE_TASK_RUNNER_H_