Add a stub implementation for Mojo AudioDecoder interface

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.
     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(AudioDecoderConfig config, int32 cdm_id)
+  Initialize(AudioDecoderClient client, AudioDecoderConfig config, int32 cdm_id)
      => (bool success, bool needs_bitstream_conversion);
 
   // 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);
 };