Rework FileWatcher to avoid race condition upon deletion.

chrome/browser/file_watcher_mac.cc

 // Copyright (c) 2009 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.
 
 #include "chrome/browser/file_watcher.h"
 
 #include <CoreServices/CoreServices.h>
 
 #include "base/file_path.h"
 #include "base/file_util.h"
@@ skipping 58 matching lines @@
       // much rather than miss a notification.
       delegate_->OnFileChanged(path_);
     } else if (!file_exists && !last_modified_.is_null()) {
       last_modified_ = base::Time();
       delegate_->OnFileChanged(path_);
     }
   }
 
  private:
   // Delegate to notify upon changes.
-  FileWatcher::Delegate* delegate_;
+  scoped_refptr<FileWatcher::Delegate> delegate_;
 
   // Path we're watching (passed to delegate).
   FilePath path_;
 
   // Backend stream we receive event callbacks from (strong reference).
   FSEventStreamRef fsevent_stream_;
 
   // Keep track of the last modified time of the file.  We use nulltime
   // to represent the file not existing.
   base::Time last_modified_;
@@ skipping 58 matching lines @@
   FSEventStreamStart(fsevent_stream_);
 
   return true;
 }
 
 }  // namespace
 
 FileWatcher::FileWatcher() {
   impl_ = new FileWatcherImpl();
 }