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

base/message_loop/message_loop.h

Index: base/message_loop/message_loop.h
diff --git a/base/message_loop/message_loop.h b/base/message_loop/message_loop.h
index 3445a77aa598c7de2159a8f8f5c4add2e376b24a..9429e6b7115a24c02dc32e7d32653dc1b75236ea 100644
--- a/base/message_loop/message_loop.h
+++ b/base/message_loop/message_loop.h
@@ -296,16 +296,9 @@
   const std::string& thread_name() const { return thread_name_; }
 
   // Gets the TaskRunner associated with this message loop.
-  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);
+  // 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_; }
 
   // Enables or disables the recursive task processing. This happens in the case
   // of recursive message loops. Some unwanted message loop may occurs when
@@ -528,11 +521,8 @@
 
   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<SingleThreadTaskRunner> task_runner_;
+  scoped_refptr<internal::MessageLoopTaskRunner> task_runner_;
   scoped_ptr<ThreadTaskRunnerHandle> thread_task_runner_handle_;
 
   template <class T, class R> friend class base::subtle::DeleteHelperInternal;