base: Make it possible to replace the MessageLoop's task runner

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 278 matching lines @@
   Type type() const { return type_; }
 
   // Optional call to connect the thread name with this loop.
   void set_thread_name(const std::string& thread_name) {
     DCHECK(thread_name_.empty()) << "Should not rename this thread!";
     thread_name_ = thread_name;
   }
   const std::string& thread_name() const { return thread_name_; }
 
   // Gets the TaskRunner associated with this message loop.
-  // TODO(skyostil): Change this to return a const reference to a refptr
-  // once the internal type matches what is being returned (crbug.com/465354).
-  scoped_refptr<SingleThreadTaskRunner> task_runner() { return task_runner_; }
+  const scoped_refptr<SingleThreadTaskRunner>& task_runner() {
+    return task_runner_;
+  }
+
+  // Sets a new TaskRunner for this message loop. The message loop must already
+  // have been bound to a thread prior to this call, and the task runner must
+  // belong to that thread. Note that changing the task runner will also affect
+  // the ThreadTaskRunnerHandle for the target thread. Must be called on the
+  // thread to which the message loop is bound.
+  void SetTaskRunner(scoped_refptr<SingleThreadTaskRunner> task_runner);
 
   // Enables or disables the recursive task processing. This happens in the case
   // of recursive message loops. Some unwanted message loop may occurs when
   // using common controls or printer functions. By default, recursive task
   // processing is disabled.
   //
   // Please utilize |ScopedNestableTaskAllower| instead of calling these methods
   // directly.  In general nestable message loops are to be avoided.  They are
   // dangerous and difficult to get right, so please use with extreme caution.
   //
@@ skipping 107 matching lines @@
       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();
 
+  // Sets the ThreadTaskRunnerHandle for the current thread to point to the
+  // task runner for this message loop.
+  void SetThreadTaskRunnerHandle();
+
   // 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);
 
@@ skipping 75 matching lines @@
   HistogramBase* message_histogram_;
 
   RunLoop* run_loop_;
 
   ObserverList<TaskObserver> task_observers_;
 
   debug::TaskAnnotator task_annotator_;
 
   scoped_refptr<internal::IncomingTaskQueue> incoming_task_queue_;
 
+  // A task runner which we haven't bound to a thread yet.
+  scoped_refptr<internal::MessageLoopTaskRunner> unbound_task_runner_;
+
   // The task runner associated with this message loop.
-  scoped_refptr<internal::MessageLoopTaskRunner> task_runner_;
+  scoped_refptr<SingleThreadTaskRunner> task_runner_;
   scoped_ptr<ThreadTaskRunnerHandle> thread_task_runner_handle_;
 
   template <class T, class R> friend class base::subtle::DeleteHelperInternal;
   template <class T, class R> friend class base::subtle::ReleaseHelperInternal;
 
   void DeleteSoonInternal(const tracked_objects::Location& from_here,
                           void(*deleter)(const void*),
                           const void* object);
   void ReleaseSoonInternal(const tracked_objects::Location& from_here,
                            void(*releaser)(const void*),
@@ skipping 137 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_