Reduce usage of MessageLoopProxy in base/

base/single_thread_task_runner.h

Index: base/single_thread_task_runner.h
diff --git a/base/single_thread_task_runner.h b/base/single_thread_task_runner.h
index e82941a348a723fad0199b6ebaeac383f475fb17..8802617be8187a7452bb2f3221b76211b554255e 100644
--- a/base/single_thread_task_runner.h
+++ b/base/single_thread_task_runner.h
@@ -16,7 +16,8 @@ namespace base {
 // 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 Task Runner (see
+//     ThreadTaskRunnerHandle).
 //   - 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