Run ScopedTaskScheduler tasks synchronously.

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 <memory>
 #include <queue>
 #include <string>
@@ skipping 216 matching lines @@
     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);
 
+  // Clears task_runner() and the ThreadTaskRunnerHandle for the target thread.
+  // Must be called on the thread to which the message loop is bound.
+  void ClearTaskRunnerForTesting();
+
   // Enables or disables the recursive task processing. This happens in the case
   // of recursive message loops. Some unwanted message loops may occur when
   // using common controls or printer functions. By default, recursive task
   // processing is disabled.
   //
   // Please use |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 358 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.
 static_assert(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
               "MessageLoopForIO should not have extra member variables");
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_