Update PluginInstance for audio support for content decryption.

media/base/decryptor.h

Index: media/base/decryptor.h
diff --git a/media/base/decryptor.h b/media/base/decryptor.h
index f01b8cc57cd570753d169d32c23ce72e4bacc494..37f5e7ab3a9f7ec48fe6f4b773474859c5b5a751 100644
--- a/media/base/decryptor.h
+++ b/media/base/decryptor.h
@@ -137,6 +137,7 @@ class MEDIA_EXPORT Decryptor {
                                       const KeyAddedCB& key_added_cb) = 0;
 
   // Helper structure for managing multiple decoded audio buffers per input.
+  // TODO(xhwang): Rename this to AudioFrames.
   typedef std::list<scoped_refptr<Buffer> > AudioBuffers;
 
   // Indicates completion of audio/video decrypt-and-decode operation.