Revert of base: Remove use of MessageLoopProxy

base/files/file_path_watcher.h

Index: base/files/file_path_watcher.h
diff --git a/base/files/file_path_watcher.h b/base/files/file_path_watcher.h
index 4f132aff78a9ff1ecaaac08ec945d0adc8028a49..d26fa060446cad94cf5c04d027eacac3931489fe 100644
--- a/base/files/file_path_watcher.h
+++ b/base/files/file_path_watcher.h
@@ -12,7 +12,7 @@
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
-#include "base/single_thread_task_runner.h"
+#include "base/message_loop/message_loop_proxy.h"
 
 namespace base {
 
@@ -58,13 +58,12 @@
     // check |is_cancelled()| to avoid duplicate work.
     virtual void CancelOnMessageLoopThread() = 0;
 
-    scoped_refptr<base::SingleThreadTaskRunner> task_runner() const {
-      return task_runner_;
+    scoped_refptr<base::MessageLoopProxy> message_loop() const {
+      return message_loop_;
     }
 
-    void set_task_runner(
-        scoped_refptr<base::SingleThreadTaskRunner> task_runner) {
-      task_runner_ = task_runner.Pass();
+    void set_message_loop(const scoped_refptr<base::MessageLoopProxy>& loop) {
+      message_loop_ = loop;
     }
 
     // Must be called before the PlatformDelegate is deleted.
@@ -77,7 +76,7 @@
     }
 
    private:
-    scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+    scoped_refptr<base::MessageLoopProxy> message_loop_;
     bool cancelled_;
   };