Introduce task_runner() accessors for both base::Thread and base::MessageLoop

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 277 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 message loop proxy associated with this message loop.
+  //
+  // NOTE: Deprecated; prefer task_runner() and the TaskRunner interfaces
   scoped_refptr<MessageLoopProxy> message_loop_proxy() {
     return message_loop_proxy_;
   }
 
+  // Gets the TaskRunner associated with this message loop.
+  scoped_refptr<SingleThreadTaskRunner> task_runner() {
+    return message_loop_proxy_;
+  }
+
   // 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.
   //
   // The specific case where tasks get queued is:
@@ skipping 334 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_