components: Introduce AlarmTimer class and use it for GCM heartbeat

components/timers/alarm_timer.h

Index: components/timers/alarm_timer.h
diff --git a/components/timers/alarm_timer.h b/components/timers/alarm_timer.h
new file mode 100644
index 0000000000000000000000000000000000000000..f43a4fb9348852d8faa76af3180ca3f8ebaf7257
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+++ b/components/timers/alarm_timer.h
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+// Copyright 2014 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_TIMER_ALARM_TIMER_H_
+#define COMPONENTS_TIMER_ALARM_TIMER_H_
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/message_loop/message_loop.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+
+namespace base {
+struct PendingTask;
+}
+
+namespace timers {
+// The class implements a timer that is capable of waking the system up from a
+// suspended state.  For example, this is useful for running tasks that are
+// needed for maintaining network connectivity, like sending heartbeat messages.
+// Currently, this feature is only available on Chrome OS systems running linux
+// version 3.11 or higher.  On all other platforms, the AlarmTimer behaves
+// exactly the same way as a regular Timer.
+class AlarmTimer : public base::Timer,
+                   public base::MessageLoop::DestructionObserver {
+ public:
+  // The delegate is responsible for managing the system level details for
+  // actually setting up and monitoring a timer that is capable of waking the
+  // system from suspend.  This class is reference counted because it may need
+  // to outlive the timer in order to clean up after itself.
+  class Delegate : public base::RefCountedThreadSafe<Delegate> {
+   public:
+    // Initializes the timer.  Should return true iff the system has timers that
+    // can wake it up from suspend.  Will only be called once.
+    virtual bool Init(base::WeakPtr<AlarmTimer> timer) = 0;
+
+    // Stops the currently running timer.  It should be safe to call this more
+    // than once.
+    virtual void Stop() = 0;
+
+    // Resets the timer to fire after |delay| has passed.  Cancels any
+    // pre-existing delay.
+    virtual void Reset(base::TimeDelta delay) = 0;
+
+   protected:
+    virtual ~Delegate() {}
+
+   private:
+    friend class base::RefCountedThreadSafe<Delegate>;
+  };
+
+  AlarmTimer(bool retain_user_task, bool is_repeating);
+
+  AlarmTimer(const tracked_objects::Location& posted_from,
+             base::TimeDelta delay,
+             const base::Closure& user_task,
+             bool is_repeating);
+
+  virtual ~AlarmTimer();
+
+  // Timer overrides.
+  void Stop() override;
+  void Reset() override;
+
+  // MessageLoop::DestructionObserver overrides.
+  void WillDestroyCurrentMessageLoop() override;
+
+  // Must be called by the delegate to indicate that the timer has fired and
+  // that the user task should be run.
+  void OnTimerFired();
+
+ private:
+  // Initializes the timer with the appropriate delegate.
+  void Init();
+
+  // Delegate that will manage actually setting the timer.
+  scoped_refptr<Delegate> delegate_;
+
+  // Keeps track of the user task we want to run.  A new one is constructed
+  // every time Reset() is called.
+  scoped_ptr<base::PendingTask> pending_task_;
+
+  // Tracks whether the timer has the ability to wake the system up from
+  // suspend.  This is a runtime check because we won't know if the system
+  // supports being woken up from suspend until the delegate actually tries to
+  // set it up.
+  bool can_wake_from_suspend_;
+
+  // Pointer to the message loop that started the timer.  Used to track the
+  // destruction of that message loop.
+  base::MessageLoop* origin_message_loop_;
+
+  base::WeakPtrFactory<AlarmTimer> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(AlarmTimer);
+};
+
+}  // namespace timers
+
+#endif  // COMPONENTS_TIMER_ALARM_TIMER_H_