Revert "Revert 285479 "Make DataSource::Stop() synchronous.""

chrome/utility/media_galleries/ipc_data_source.h

Index: chrome/utility/media_galleries/ipc_data_source.h
diff --git a/chrome/utility/media_galleries/ipc_data_source.h b/chrome/utility/media_galleries/ipc_data_source.h
index c65c457d840339a227314b7a77da4a1ba465becb..6fb3b76a58645e56687e15b4b74ee0a786e9da9b 100644
--- a/chrome/utility/media_galleries/ipc_data_source.h
+++ b/chrome/utility/media_galleries/ipc_data_source.h
@@ -32,7 +32,7 @@ class IPCDataSource: public media::DataSource,
 
   // Implementation of DataSource. These methods may be called on any single
   // thread. First usage of these methods attaches a thread checker.
-  virtual void Stop(const base::Closure& callback) OVERRIDE;
+  virtual void Stop() OVERRIDE;
   virtual void Read(int64 position, int size, uint8* data,
                     const ReadCB& read_cb) OVERRIDE;
   virtual bool GetSize(int64* size_out) OVERRIDE;