[Cast] Add MultizoneAudioDecoderProxy Skeleton

This CL adds a new class skeleton, to be implemented in a future CL and used in
AudioPipelineImpl and CastAudioOutputStream.

Bug: b/167424911

Change-Id: I3dd799f29808a5046b983195120df393b1514510
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401305Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Commit-Queue: Ryan Keane <rwkeane@google.com>
Cr-Commit-Position: refs/heads/master@{#805861}

chromecast/media/BUILD.gn

@@ -47,6 +47,9 @@ group("libcast_media") {
     deps = [ "//chromecast/media/cma/backend:libcast_media_1.0" ]
   }
 
+  # TODO(rwkeane): Condition on build flag.
+  deps += [ "//chromecast/media/cma/backend/proxy" ]
+
   if (cast_volume_control_in_avsettings) {
     deps += [ "//chromecast/media/avsettings:libcast_avsettings_1.0" ]
   }

chromecast/media/cma/backend/proxy/BUILD.gn

+# Copyright 2020 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.
+
+import("//chromecast/chromecast.gni")
+
+cast_source_set("proxy") {
+  sources = [
+    "multizone_audio_decoder_proxy.cc",
+    "multizone_audio_decoder_proxy.h",
+  ]
+
+  deps = [
+    "//base",
+    "//chromecast/base",
+    "//chromecast/media/api",
+    "//chromecast/public/media",
+  ]
+}

chromecast/media/cma/backend/proxy/multizone_audio_decoder_proxy.cc

+// Copyright 2020 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.
+
+#include "chromecast/media/cma/backend/proxy/multizone_audio_decoder_proxy.h"
+
+#include "base/notreached.h"
+#include "chromecast/public/media/decoder_config.h"
+
+namespace chromecast {
+namespace media {
+
+void MultizoneAudioDecoderProxy::SetDelegate(Delegate* delegate) {
+  NOTREACHED();
+}
+
+MultizoneAudioDecoderProxy::BufferStatus MultizoneAudioDecoderProxy::PushBuffer(
+    scoped_refptr<DecoderBufferBase> buffer) {
+  NOTREACHED();
+  return BufferStatus::kBufferSuccess;
+}
+
+bool MultizoneAudioDecoderProxy::SetConfig(const AudioConfig& config) {
+  NOTREACHED();
+  return true;
+}
+
+bool MultizoneAudioDecoderProxy::SetVolume(float multiplier) {
+  NOTREACHED();
+  return true;
+}
+
+MultizoneAudioDecoderProxy::RenderingDelay
+MultizoneAudioDecoderProxy::GetRenderingDelay() {
+  NOTREACHED();
+  return RenderingDelay{};
+}
+
+void MultizoneAudioDecoderProxy::GetStatistics(Statistics* statistics) {
+  NOTREACHED();
+}
+
+bool MultizoneAudioDecoderProxy::RequiresDecryption() {
+  NOTREACHED();
+  return true;
+}
+
+void MultizoneAudioDecoderProxy::SetObserver(Observer* observer) {
+  NOTREACHED();
+}
+
+}  // namespace media
+}  // namespace chromecast

chromecast/media/cma/backend/proxy/multizone_audio_decoder_proxy.h

+// Copyright 2020 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.
+
+#ifndef CHROMECAST_MEDIA_CMA_BACKEND_PROXY_MULTIZONE_AUDIO_DECODER_PROXY_H_
+#define CHROMECAST_MEDIA_CMA_BACKEND_PROXY_MULTIZONE_AUDIO_DECODER_PROXY_H_
+
+#include "base/memory/ref_counted.h"
+#include "chromecast/media/api/cma_backend.h"
+#include "chromecast/media/api/decoder_buffer_base.h"
+
+namespace chromecast {
+namespace media {
+
+struct AudioConfig;
+
+// This class is used to decrypt then proxy audio data to an external
+// CmaBackend::AudioDecoder over gRPC.
+class MultizoneAudioDecoderProxy : public CmaBackend::AudioDecoder {
+ public:
+  using BufferStatus = CmaBackend::Decoder::BufferStatus;
+  using Delegate = CmaBackend::Decoder::Delegate;
+  using Observer = CmaBackend::AudioDecoder::Observer;
+  using RenderingDelay = CmaBackend::AudioDecoder::RenderingDelay;
+  using Statistics = CmaBackend::AudioDecoder::Statistics;
+
+  ~MultizoneAudioDecoderProxy() override;
+
+  // CmaBackend::AudioDecoder implementation:
+  void SetDelegate(Delegate* delegate) override;
+  BufferStatus PushBuffer(scoped_refptr<DecoderBufferBase> buffer) override;
+  bool SetConfig(const AudioConfig& config) override;
+  bool SetVolume(float multiplier) override;
+  RenderingDelay GetRenderingDelay() override;
+  void GetStatistics(Statistics* statistics) override;
+  bool RequiresDecryption() override;
+  void SetObserver(Observer* observer) override;
+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_MEDIA_CMA_BACKEND_PROXY_MULTIZONE_AUDIO_DECODER_PROXY_H_