Reland of Make AudioSinkInterface::Data hold a const pointer to the audio buffer.

webrtc/api/call/audio_sink.h

Index: webrtc/api/call/audio_sink.h
diff --git a/webrtc/api/call/audio_sink.h b/webrtc/api/call/audio_sink.h
index e865ead365cdc68e2ec50a2b4a2a0c607a26990d..8d38763f9402e6e6a351c3a051ad5cd72c210e76 100644
--- a/webrtc/api/call/audio_sink.h
+++ b/webrtc/api/call/audio_sink.h
@@ -27,7 +27,7 @@
   virtual ~AudioSinkInterface() {}
 
   struct Data {
-    Data(int16_t* data,
+    Data(const int16_t* data,
          size_t samples_per_channel,
          int sample_rate,
          size_t channels,
@@ -38,7 +38,7 @@
           channels(channels),
           timestamp(timestamp) {}
 
-    int16_t* data;               // The actual 16bit audio data.
+    const int16_t* data;         // The actual 16bit audio data.
     size_t samples_per_channel;  // Number of frames in the buffer.
     int sample_rate;             // Sample rate in Hz.
     size_t channels;             // Number of channels in the audio data.