Change PPB_VideoWriter Open function to return stream_id as out param.

ppapi/cpp/video_reader.h

 // Copyright (c) 2013 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.
 
 #ifndef PPAPI_CPP_VIDEO_READER_H_
 #define PPAPI_CPP_VIDEO_READER_H_
 
 #include <string>
 
 #include "ppapi/c/pp_time.h"
@@ skipping 26 matching lines @@
   VideoReader(const VideoReader& other);
 
   /// A constructor used when you have received a PP_Resource as a return
   /// value that has had its reference count incremented for you.
   ///
   /// @param[in] resource A PP_Resource corresponding to a video reader.
   VideoReader(PassRef, PP_Resource resource);
 
   /// Opens a stream for reading video and associates it with the given id.
   ///
-  /// @param[in] stream_id A string uniquely identifying the stream to read
-  /// from.
+  /// @param[in] stream_id A <code>Var</code> uniquely identifying the stream
+  /// to read from.
   /// @param[in] callback A <code>CompletionCallback</code> to be called upon
   /// completion of Open.
   ///
   /// @return A return code from <code>pp_errors.h</code>.
-  int32_t Open(const std::string& stream_id,
+  int32_t Open(const Var& stream_id,
                const CompletionCallback& cc);
 
   /// Gets the next frame of video from the reader's stream.
   ///
   /// @param[in] callback A <code>CompletionCallbackWithOutput</code> to be
   /// called upon completion of GetNextFrame.
   ///
   /// @return A return code from <code>pp_errors.h</code>.
   int32_t GetFrame(const CompletionCallbackWithOutput<VideoFrame>& cc);
 
   /// Closes the reader's current stream.
   void Close();
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_VIDEO_READER_H_