Added support for changing the volume of AudioTrack as discussed in BUG=webrtc:6533

webrtc/sdk/android/api/org/webrtc/AudioTrack.java

Index: webrtc/sdk/android/api/org/webrtc/AudioTrack.java
diff --git a/webrtc/sdk/android/api/org/webrtc/AudioTrack.java b/webrtc/sdk/android/api/org/webrtc/AudioTrack.java
index c33a9d8db1d83aa1988520119361afc7284c414d..3ae9e6fdb5b705d28edab15d82b9653ef2f43010 100644
--- a/webrtc/sdk/android/api/org/webrtc/AudioTrack.java
+++ b/webrtc/sdk/android/api/org/webrtc/AudioTrack.java
@@ -12,7 +12,19 @@ package org.webrtc;
 
 /** Java wrapper for a C++ AudioTrackInterface */
 public class AudioTrack extends MediaStreamTrack {
+  final long nativeTrack;

[magjed_webrtc, 2017/04/05 19:14:00]

No need to introduce a new member variable, just use the nativeTrack in the
super class MediaStreamTrack instead.

+
   public AudioTrack(long nativeTrack) {
     super(nativeTrack);
+    this.nativeTrack = nativeTrack;
+  }
+
+  /** Sets the volume for the underlying MediaSource. Volume is a gain value in the range
+   *  0 to 10.
+   */
+  public void setVolume(double volume) {
+    nativeSetVolume(nativeTrack, volume);
   }
+
+  private static native void nativeSetVolume(long nativeTrack, double volume);
 }