[Chromecast] Implement new volume control API

chromecast/media/cma/backend/alsa/slew_volume.h

 // 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.
 
 // Scale volume with slew rate limiting
 
 #ifndef CHROMECAST_MEDIA_CMA_BACKEND_ALSA_SLEW_VOLUME_H_
 #define CHROMECAST_MEDIA_CMA_BACKEND_ALSA_SLEW_VOLUME_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 
 namespace chromecast {
 namespace media {
 
 class SlewVolume {
  public:
   SlewVolume();
   SlewVolume(int max_slew_up_ms, int max_slew_down_ms);
   ~SlewVolume() = default;
 
   void SetSampleRate(int sample_rate);
   void SetVolume(double volume_scale);
 
+  // Called to indicate that the stream was interrupted; volume changes can be
+  // applied immediately.
+  void Interrupted();
+
   // Assumes 1 channel float data that is 16-byte aligned. Smoothly calculates
   // dest[i] += src[i] * volume_scaling
   // ProcessFMAC will be called once for each channel of audio present and
   // |repeat_transition| will be true for channels 2 through n.
   void ProcessFMAC(bool repeat_transition,
                    const float* src,
                    int frames,
                    float* dest);
 
   // Assumes 2 channels.
   bool ProcessInterleaved(int32_t* data, int frames);
 
  private:
   double sample_rate_;
   double volume_scale_ = 1.0;
   double current_volume_ = 1.0;
   double last_starting_volume_ = 1.0;
   int max_slew_time_up_ms_;
   int max_slew_time_down_ms_;
   double max_slew_up_;
   double max_slew_down_;
+  bool interrupted_ = true;
 
   DISALLOW_COPY_AND_ASSIGN(SlewVolume);
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_CMA_BACKEND_ALSA_SLEW_VOLUME_H_