Use data pipe for encoded buffers in MojoAudioDecoder

media/mojo/interfaces/audio_decoder.mojom

 // Copyright 2016 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.
 
 module media.interfaces;
 
 import "media/mojo/interfaces/media_types.mojom";
 
 interface AudioDecoder {
   // Status of a decode operation. See media::AudioDecoder for description.
   enum DecodeStatus {
     OK,            // We're all good.
     ABORTED,       // We aborted as a result of Reset() or destruction.
     DECODE_ERROR,  // A decoding error occurred.
   };
 
   // Initializes the AudioDecoder with the audio codec configuration and CDM id.
   // For the unencrypted streams the |cdm_id| is ignored. Executed the callback
   // with whether the initialization succeeded, and whether the pipeline needs
   // bitstream conversion.
   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
   // pipeline can send next buffer to decode.
   // If |buffer| is an EOS buffer then the decoder must be flushed, i.e. all
   // pending buffers should be processed, the corresponding decoded buffers
   // should be returned to the proxy, and only then the service should return
   // DecoderStatus.
   Decode(DecoderBuffer buffer) => (DecodeStatus status);
 
   // Resets decoder state. Should be called only if Initialize() succeeds.
   // All pending Decode() requests will be finished or aborted, then the method
   // executes the callback.
   Reset() => ();
 };
 
 interface AudioDecoderClient {
   // Sends the decoded audio buffer back to the proxy.
   OnBufferDecoded(AudioBuffer buffer);
 };