Lazily initialize MessageLoop for faster thread startup

base/message_loop/incoming_task_queue.h

Index: base/message_loop/incoming_task_queue.h
diff --git a/base/message_loop/incoming_task_queue.h b/base/message_loop/incoming_task_queue.h
index 72e1f30282966de72b01a505a6144839a1d00643..7dd1e82312914cec00e239aa4698cada7307cb1c 100644
--- a/base/message_loop/incoming_task_queue.h
+++ b/base/message_loop/incoming_task_queue.h
@@ -53,6 +53,10 @@ class BASE_EXPORT IncomingTaskQueue
   // Disconnects |this| from the parent message loop.
   void WillDestroyCurrentMessageLoop();
 
+  // This should be called when the message loop becomes ready for
+  // scheduling work.
+  void StartScheduling();
+
  private:
   friend class RefCountedThreadSafe<IncomingTaskQueue>;
   virtual ~IncomingTaskQueue();
@@ -66,6 +70,9 @@ class BASE_EXPORT IncomingTaskQueue
   // does not retain |pending_task->task| beyond this function call.
   bool PostPendingTask(PendingTask* pending_task);
 
+  // Wakes up the message loop and schedules work.
+  void ScheduleWork();
+
   // Number of tasks that require high resolution timing. This value is kept
   // so that ReloadWorkQueue() completes in constant time.
   int high_res_task_count_;
@@ -92,6 +99,9 @@ class BASE_EXPORT IncomingTaskQueue
   // if the incoming queue was not empty.
   const bool always_schedule_work_;
 
+  // False until StartScheduling() is called.
+  bool is_ready_for_scheduling_;
+
   DISALLOW_COPY_AND_ASSIGN(IncomingTaskQueue);
 };