components: Introduce AlarmTimer class and use it for GCM heartbeat

base/timer/alarm_timer.h

Index: base/timer/alarm_timer.h
diff --git a/base/timer/alarm_timer.h b/base/timer/alarm_timer.h
new file mode 100644
index 0000000000000000000000000000000000000000..8ba818301c848d0848bf1533379c1c8d0cd50faf
--- /dev/null
+++ b/base/timer/alarm_timer.h
@@ -0,0 +1,104 @@
+// 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 BASE_TIMER_ALARM_TIMER_CHROMEOS_H_
+#define BASE_TIMER_ALARM_TIMER_CHROMEOS_H_
+
+#include "base/base_export.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;
+
+// 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 BASE_EXPORT AlarmTimer : public Timer,
+                               public 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 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(WeakPtr<AlarmTimer> timer) = 0;
+
+    // Stop the currently running timer.  It should be safe to call this more

[Daniel Erat, 2014/10/15 15:04:22]

nit: s/Stop/Stops/

[Chirantan Ekbote, 2014/10/16 21:26:38]

Done.

+    // than once.
+    virtual void Stop() = 0;
+
+    // Reset the timer to fire after |delay| amount of time has passed.  Cancels

[Daniel Erat, 2014/10/15 15:04:22]

nit: s/Reset/Resets/; can also remove "amount of time" here

[Chirantan Ekbote, 2014/10/16 21:26:38]

Done.

+    // any pre-existing delay.
+    virtual void Reset(TimeDelta delay) = 0;
+
+   protected:
+    virtual ~Delegate() {};
+
+   private:
+    friend class RefCountedThreadSafe<Delegate>;
+  };
+
+  AlarmTimer(bool retain_user_task, bool is_repeating);
+
+  AlarmTimer(const tracked_objects::Location& posted_from,
+             TimeDelta delay,
+             const Closure& user_task,
+             bool is_repeating);
+
+  virtual ~AlarmTimer();
+
+  // Timer overrides.
+  virtual bool IsRunning() const override;
+  virtual TimeDelta GetCurrentDelay() const override;
+  virtual void Start(const tracked_objects::Location& posted_from,
+                     TimeDelta delay,
+                     const Closure& user_task) override;
+  virtual void Stop() override;
+  virtual void Reset() override;
+
+  // MessageLoop::DestructionObserver overrides.
+  virtual 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:
+  // 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 timer Reset() is called.
+  scoped_ptr<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.
+  MessageLoop* origin_message_loop_;
+
+  WeakPtrFactory<AlarmTimer> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(AlarmTimer);
+};
+
+}  // namespace base

[Daniel Erat, 2014/10/15 15:04:22]

nit: add blank line after this one

[Chirantan Ekbote, 2014/10/16 21:26:38]

Done.

+#endif  // BASE_TIMER_ALARM_TIMER_CHROMEOS_H_