Software volume control hook-up in linux.

media/audio/linux/alsa_output.h

 // Copyright (c) 2009 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.
 //
 // Creates an output stream based on the ALSA PCM interface.  The current
 // implementation creates one thread per ALSA playback handle that is
 // responsible for synchronously pulling data from the audio data source.
 //
 // This output stream buffers in two places:
 //   (1) In the ALSA device
@@ skipping 141 matching lines @@
   size_t packet_size_;
 
   // Flag indiciating the device write tasks have stopped scheduling
   // themselves.  This should only be modified by the BufferPackets() and
   // FillAlsaDeviceBuffer() methods.
   bool device_write_suspended_;
 
   // Flag indicating that the resources are already cleaned.
   bool resources_released_;
 
+  // Volume level from 0 to 1.
+  float volume_;
+
   DISALLOW_COPY_AND_ASSIGN(AlsaPCMOutputStream);
 };
 
 #endif  // MEDIA_AUDIO_LINUX_ALSA_OUTPUT_H_