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..0d2d6b0058a2f2ae3bf946de123bb569d36e8f6d 100644
--- a/base/message_loop/incoming_task_queue.h
+++ b/base/message_loop/incoming_task_queue.h
@@ -26,6 +26,11 @@ class BASE_EXPORT IncomingTaskQueue
  public:
   explicit IncomingTaskQueue(MessageLoop* message_loop);
 
+  // Creates a task queue for the message loop that is to be initialized lazily
+  // (i.e. created by CreateForLazyInit()).
+  static IncomingTaskQueue* CreateForLazyInitMessageLoop(
+      MessageLoop* message_loop);
+
   // Appends a task to the incoming queue. Posting of all tasks is routed though
   // AddToIncomingQueue() or TryAddToIncomingQueue() to make sure that posting
   // task is properly synchronized between different threads.
@@ -53,6 +58,13 @@ class BASE_EXPORT IncomingTaskQueue
   // Disconnects |this| from the parent message loop.
   void WillDestroyCurrentMessageLoop();
 
+  // Called when |message_loop_|'s LazyInit() is called, so that now it's ready
+  // for scheduling work. It is not valid to call this unless this task queue
+  // is created by CreateForLazyInitMessageLoop().
+  void DidInitializeMessageLoop();
+
+  bool empty();
+
  private:
   friend class RefCountedThreadSafe<IncomingTaskQueue>;
   virtual ~IncomingTaskQueue();
@@ -92,6 +104,11 @@ class BASE_EXPORT IncomingTaskQueue
   // if the incoming queue was not empty.
   const bool always_schedule_work_;
 
+  // True if our message loop is created for lazy initialization and hasn't been
+  // initialized yet. Note that while this is true this task queue won't call
+  // ScheduleWork even if always_schedule_work_ is true.
+  bool message_loop_not_initialized_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(IncomingTaskQueue);
 };