[Chromecast] Add support for different playback rates to ALSA backend

chromecast/media/cma/backend/alsa/media_pipeline_backend_alsa.cc

 // Copyright 2015 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/alsa/media_pipeline_backend_alsa.h"
 
 #include <limits>
 
 #include "chromecast/base/task_runner_impl.h"
 #include "chromecast/media/cma/backend/alsa/audio_decoder_alsa.h"
@@ skipping 63 matching lines @@
 
 bool MediaPipelineBackendAlsa::Resume() {
   DCHECK_EQ(kStatePaused, state_);
   if (audio_decoder_ && !audio_decoder_->Resume())
     return false;
   state_ = kStatePlaying;
   return true;
 }
 
 bool MediaPipelineBackendAlsa::SetPlaybackRate(float rate) {
-  // TODO(kmackay) Implement this for rates other than 1.0.
-  if (rate != 1.0)
-    NOTIMPLEMENTED() << " unhandled rate: " << rate;
+  if (audio_decoder_) {
+    return audio_decoder_->SetPlaybackRate(rate);
+  }
   return true;
 }
 
 int64_t MediaPipelineBackendAlsa::GetCurrentPts() {
   if (audio_decoder_)
     return audio_decoder_->current_pts();
   return std::numeric_limits<int64_t>::min();
 }
 
 bool MediaPipelineBackendAlsa::Primary() const {
   return (params_.audio_type !=
           MediaPipelineDeviceParams::kAudioStreamSoundEffects);
 }
 
 const scoped_refptr<base::SingleThreadTaskRunner>&
 MediaPipelineBackendAlsa::GetTaskRunner() const {
   return static_cast<TaskRunnerImpl*>(params_.task_runner)->runner();
 }
 
 }  // namespace media
 }  // namespace chromecast