Add video decoding methods in Decryptor and add DecryptingVideoDecoder.

media/base/video_decoder.h

Index: media/base/video_decoder.h
diff --git a/media/base/video_decoder.h b/media/base/video_decoder.h
index 4c8621752d8a99b41f587f76bd5d078c9e4d801e..915a9b429ff7eef23bcca28d03b1b815fe848bda 100644
--- a/media/base/video_decoder.h
+++ b/media/base/video_decoder.h
@@ -28,7 +28,8 @@ class MEDIA_EXPORT VideoDecoder
 
   // Initializes a VideoDecoder with the given DemuxerStream, executing the
   // |status_cb| upon completion.
-  // |statistics_cb| is used to update global pipeline statistics.
+  // |statistics_cb| is used to update the global pipeline statistics.
+  // Note: No VideoDecoder calls should be made before |status_cb| is executed.
   virtual void Initialize(const scoped_refptr<DemuxerStream>& stream,
                           const PipelineStatusCB& status_cb,
                           const StatisticsCB& statistics_cb) = 0;
@@ -53,6 +54,7 @@ class MEDIA_EXPORT VideoDecoder
   // Resets decoder state, fulfilling all pending ReadCB and dropping extra
   // queued decoded data. After this call, the decoder is back to an initialized
   // clean state.
+  // Note: No VideoDecoder calls should be made before |closure| is executed.
   virtual void Reset(const base::Closure& closure) = 0;
 
   // Stops decoder, fires any pending callbacks and sets the decoder to an