components: Introduce AlarmTimer class and use it for GCM heartbeat

base/timer/timer.h

Index: base/timer/timer.h
diff --git a/base/timer/timer.h b/base/timer/timer.h
index 6d282ee8e7ac84f3d6f5757650c08be70463f9e6..e6d998fe4f5cd10bb58c75c6e6155c4364b17754 100644
--- a/base/timer/timer.h
+++ b/base/timer/timer.h
@@ -114,6 +114,32 @@ class BASE_EXPORT Timer {
   bool retain_user_task() const { return retain_user_task_; }
   bool is_repeating() const { return is_repeating_; }
 
+  // Location in user code.
+  tracked_objects::Location posted_from_;
+  // Delay requested by user.
+  TimeDelta delay_;
+  // user_task_ is what the user wants to be run at desired_run_time_.
+  base::Closure user_task_;
+
+  // The desired run time of user_task_. The user may update this at any time,
+  // even if their previous request has not run yet. If desired_run_time_ is
+  // greater than scheduled_run_time_, a continuation task will be posted to
+  // wait for the remaining time. This allows us to reuse the pending task so as
+  // not to flood the MessageLoop with orphaned tasks when the user code
+  // excessively Stops and Starts the timer. This time can be a "zero" TimeTicks
+  // if the task must be run immediately.
+  TimeTicks desired_run_time_;
+
+  // Repeating timers automatically post the task again before calling the task
+  // callback.
+  const bool is_repeating_;
+
+  // If true, hold on to |user_task_| for reuse.
+  const bool retain_user_task_;
+
+  // If true, |user_task_| is scheduled to run sometime in the future.
+  bool is_running_;
+
  private:
   friend class BaseTimerTaskInternal;
 
@@ -139,40 +165,14 @@ class BASE_EXPORT Timer {
   // RunScheduledTask() at scheduled_run_time_.
   BaseTimerTaskInternal* scheduled_task_;
 
-  // Location in user code.
-  tracked_objects::Location posted_from_;
-  // Delay requested by user.
-  TimeDelta delay_;
-  // user_task_ is what the user wants to be run at desired_run_time_.
-  base::Closure user_task_;
-
   // The estimated time that the MessageLoop will run the scheduled_task_ that
   // will call RunScheduledTask(). This time can be a "zero" TimeTicks if the
   // task must be run immediately.
   TimeTicks scheduled_run_time_;
 
-  // The desired run time of user_task_. The user may update this at any time,
-  // even if their previous request has not run yet. If desired_run_time_ is
-  // greater than scheduled_run_time_, a continuation task will be posted to
-  // wait for the remaining time. This allows us to reuse the pending task so as
-  // not to flood the MessageLoop with orphaned tasks when the user code
-  // excessively Stops and Starts the timer. This time can be a "zero" TimeTicks
-  // if the task must be run immediately.
-  TimeTicks desired_run_time_;
-
   // Thread ID of current MessageLoop for verifying single-threaded usage.
   int thread_id_;
 
-  // Repeating timers automatically post the task again before calling the task
-  // callback.
-  const bool is_repeating_;
-
-  // If true, hold on to the user_task_ closure object for reuse.
-  const bool retain_user_task_;
-
-  // If true, user_task_ is scheduled to run sometime in the future.
-  bool is_running_;
-
   DISALLOW_COPY_AND_ASSIGN(Timer);
 };