[base] Make FilePathWatcher::Watch virtual so that it can be mocked.

base/files/file_path_watcher.h

 // Copyright (c) 2011 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.
 
 // This module provides a way to monitor a file or directory for changes.
 
 #ifndef BASE_FILES_FILE_PATH_WATCHER_H_
 #define BASE_FILES_FILE_PATH_WATCHER_H_
 #pragma once
 
@@ skipping 73 matching lines @@
     }
 
    private:
     friend class base::RefCountedThreadSafe<PlatformDelegate>;
 
     scoped_refptr<base::MessageLoopProxy> message_loop_;
     bool cancelled_;
   };
 
   FilePathWatcher();
-  ~FilePathWatcher();
+  virtual ~FilePathWatcher();
 
   // A callback that always cleans up the PlatformDelegate, either when executed
   // or when deleted without having been executed at all, as can happen during
   // shutdown.
   static void CancelWatch(const scoped_refptr<PlatformDelegate>& delegate);
 
   // Register interest in any changes on |path|. OnPathChanged will be called
   // back for each change. Returns true on success.
   // OnFilePathChanged() will be called on the same thread as Watch() is called,
   // which should have a MessageLoop of TYPE_IO.
-  bool Watch(const FilePath& path, Delegate* delegate) WARN_UNUSED_RESULT;
+  virtual bool Watch(const FilePath& path, Delegate* delegate)
+      WARN_UNUSED_RESULT;
 
  private:
   scoped_refptr<PlatformDelegate> impl_;
 
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 };
 
 }  // namespace files
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_PATH_WATCHER_H_