Revert of Reland: Lazily initialize MessageLoop for faster thread startup

base/message_loop/message_loop.h

 // Copyright 2013 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_MESSAGE_LOOP_MESSAGE_LOOP_H_
 #define BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_
 
 #include <queue>
 #include <string>
 
@@ skipping 96 matching lines @@
 #if defined(OS_ANDROID)
     TYPE_JAVA,
 #endif  // defined(OS_ANDROID)
   };
 
   // Normally, it is not necessary to instantiate a MessageLoop.  Instead, it
   // is typical to make use of the current thread's MessageLoop instance.
   explicit MessageLoop(Type type = TYPE_DEFAULT);
   // Creates a TYPE_CUSTOM MessageLoop with the supplied MessagePump, which must
   // be non-NULL.
-  explicit MessageLoop(scoped_ptr<MessagePump> pump);
-
+  explicit MessageLoop(scoped_ptr<base::MessagePump> pump);
   ~MessageLoop() override;
 
   // Returns the MessageLoop object for the current thread, or null if none.
   static MessageLoop* current();
 
   static void EnableHistogrammer(bool enable_histogrammer);
 
   typedef scoped_ptr<MessagePump> (MessagePumpFactory)();
   // Uses the given base::MessagePumpForUIFactory to override the default
   // MessagePump implementation for 'TYPE_UI'. Returns true if the factory
@@ skipping 259 matching lines @@
   // Can only be called from the thread that owns the MessageLoop.
   bool is_running() const;
 
   // Returns true if the message loop has high resolution timers enabled.
   // Provided for testing.
   bool HasHighResolutionTasks();
 
   // Returns true if the message loop is "idle". Provided for testing.
   bool IsIdleForTesting();
 
+  // Wakes up the message pump. Can be called on any thread. The caller is
+  // responsible for synchronizing ScheduleWork() calls.
+  void ScheduleWork();
+
   // Returns the TaskAnnotator which is used to add debug information to posted
   // tasks.
   debug::TaskAnnotator* task_annotator() { return &task_annotator_; }
 
   // Runs the specified PendingTask.
   void RunTask(const PendingTask& pending_task);
 
   //----------------------------------------------------------------------------
  protected:
   scoped_ptr<MessagePump> pump_;
 
  private:
   friend class RunLoop;
-  friend class internal::IncomingTaskQueue;
-  friend class ScheduleWorkTest;
-  friend class Thread;
 
-  using MessagePumpFactoryCallback = Callback<scoped_ptr<MessagePump>()>;
-
-  // Creates a MessageLoop without binding to a thread.
-  // If |type| is TYPE_CUSTOM non-null |pump_factory| must be also given
-  // to create a message pump for this message loop.  Otherwise a default
-  // message pump for the |type| is created.
-  //
-  // It is valid to call this to create a new message loop on one thread,
-  // and then pass it to the thread where the message loop actually runs.
-  // The message loop's BindToCurrentThread() method must be called on the
-  // thread the message loop runs on, before calling Run().
-  // Before BindToCurrentThread() is called only Post*Task() functions can
-  // be called on the message loop.
-  scoped_ptr<MessageLoop> CreateUnbound(
-      Type type,
-      MessagePumpFactoryCallback pump_factory);
-
-  // Common private constructor. Other constructors delegate the initialization
-  // to this constructor.
-  MessageLoop(Type type, MessagePumpFactoryCallback pump_factory);
-
-  // Configure various members and bind this message loop to the current thread.
-  void BindToCurrentThread();
+  // Configures various members for the two constructors.
+  void Init();
 
   // Invokes the actual run loop using the message pump.
   void RunHandler();
 
   // Called to process any delayed non-nestable tasks.
   bool ProcessNextDelayedNonNestableTask();
 
   // Calls RunTask or queues the pending_task on the deferred task list if it
   // cannot be run right now.  Returns true if the task was run.
   bool DeferOrRunPendingTask(const PendingTask& pending_task);
 
   // Adds the pending task to delayed_work_queue_.
   void AddToDelayedWorkQueue(const PendingTask& pending_task);
 
   // Delete tasks that haven't run yet without running them.  Used in the
   // destructor to make sure all the task's destructors get called.  Returns
   // true if some work was done.
   bool DeletePendingTasks();
 
   // Loads tasks from the incoming queue to |work_queue_| if the latter is
   // empty.
   void ReloadWorkQueue();
 
-  // Wakes up the message pump. Can be called on any thread. The caller is
-  // responsible for synchronizing ScheduleWork() calls.
-  void ScheduleWork();
-
   // Start recording histogram info about events and action IF it was enabled
   // and IF the statistics recorder can accept a registration of our histogram.
   void StartHistogrammer();
 
   // Add occurrence of event to our histogram, so that we can see what is being
   // done in a specific MessageLoop instance (i.e., specific thread).
   // If message_histogram_ is NULL, this is a no-op.
   void HistogramEvent(int event);
 
   // MessagePump::Delegate methods:
@@ skipping 33 matching lines @@
   // A recursion block that prevents accidentally running additional tasks when
   // insider a (accidentally induced?) nested message pump.
   bool nestable_tasks_allowed_;
 
 #if defined(OS_WIN)
   // Should be set to true before calling Windows APIs like TrackPopupMenu, etc
   // which enter a modal message loop.
   bool os_modal_loop_;
 #endif
 
-  // pump_factory_.Run() is called to create a message pump for this loop
-  // if type_ is TYPE_CUSTOM and pump_ is null.
-  MessagePumpFactoryCallback pump_factory_;
-
   std::string thread_name_;
   // A profiling histogram showing the counts of various messages and events.
   HistogramBase* message_histogram_;
 
   RunLoop* run_loop_;
 
   ObserverList<TaskObserver> task_observers_;
 
   debug::TaskAnnotator task_annotator_;
 
@@ skipping 151 matching lines @@
 
 // Do not add any member variables to MessageLoopForIO!  This is important b/c
 // MessageLoopForIO is often allocated via MessageLoop(TYPE_IO).  Any extra
 // data that you need should be stored on the MessageLoop's pump_ instance.
 COMPILE_ASSERT(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
                MessageLoopForIO_should_not_have_extra_member_variables);
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_