Use data pipe for encoded buffers in MojoAudioDecoder

media/mojo/interfaces/audio_decoder.mojom

Index: media/mojo/interfaces/audio_decoder.mojom
diff --git a/media/mojo/interfaces/audio_decoder.mojom b/media/mojo/interfaces/audio_decoder.mojom
index bb4f0591e2850c003bbcc8b5244c6dd4d08c2791..70a27550d1ba6e10f91f051f12f78e952723be04 100644
--- a/media/mojo/interfaces/audio_decoder.mojom
+++ b/media/mojo/interfaces/audio_decoder.mojom
@@ -21,6 +21,9 @@ interface AudioDecoder {
   Initialize(AudioDecoderClient client, AudioDecoderConfig config, int32 cdm_id)
      => (bool success, bool needs_bitstream_conversion);
 
+  // Established data connection. Should be called before Decode().
+  SetDataSource(handle<data_pipe_consumer> receive_pipe);

[xhwang, 2016/03/19 04:57:25]

See comment below. I wonder whether it'll be better to just pass the
|receive_pipe| in Initialize().

[Tima Vaisburd, 2016/03/19 22:04:46]

I considered that, but thought that we'd like to have a separate call.
Eventually we would like to have full duplex pipe, i.e. both ends, like in
MojoDecryptor. Having the separate call would make the interface cleaner. And we
can only create a pipe if we need it, although I believe you are right and the
failures will be seldom
(although right now we use init failures as a mean to query system's
capabilities). WDYT?

[xhwang, 2016/03/20 16:15:57]

You are right. I remembered that DataPipe creation actually involves an IPC to
the browser. So a separate call sgtm!

+
   // Sends the |buffer| to the underlying codec. Should be called only after
   // Initialize() succeeds. The callback with the status is called after the
   // decoder has accepted corresponding DecoderBuffer, indicating that the