base: Remove most uses of MessageLoopProxy

base/single_thread_task_runner.h

 // Copyright (c) 2012 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_SINGLE_THREAD_TASK_RUNNER_H_
 #define BASE_SINGLE_THREAD_TASK_RUNNER_H_
 
 #include "base/base_export.h"
 #include "base/sequenced_task_runner.h"
 
 namespace base {
 
 // A SingleThreadTaskRunner is a SequencedTaskRunner with one more
 // guarantee; namely, that all tasks are run on a single dedicated
 // thread.  Most use cases require only a SequencedTaskRunner, unless
 // there is a specific need to run tasks on only a single thread.
 //
 // SingleThreadTaskRunner implementations might:
-//   - Post tasks to an existing thread's MessageLoop (see MessageLoopProxy).
+//   - Post tasks to an existing thread's MessageLoop (see
+//     MessageLoop::task_runner()).
 //   - Create their own worker thread and MessageLoop to post tasks to.
 //   - Add tasks to a FIFO and signal to a non-MessageLoop thread for them to
 //     be processed. This allows TaskRunner-oriented code run on threads
 //     running other kinds of message loop, e.g. Jingle threads.
 class BASE_EXPORT SingleThreadTaskRunner : public SequencedTaskRunner {
  public:
   // A more explicit alias to RunsTasksOnCurrentThread().
   bool BelongsToCurrentThread() const {
     return RunsTasksOnCurrentThread();
   }
 
  protected:
   ~SingleThreadTaskRunner() override {}
 };
 
 }  // namespace base
 
 #endif  // BASE_SINGLE_THREAD_TASK_RUNNER_H_