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

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

Index: webrtc/sdk/android/api/org/webrtc/AudioSource.java
diff --git a/webrtc/sdk/android/api/org/webrtc/AudioSource.java b/webrtc/sdk/android/api/org/webrtc/AudioSource.java
index 99fcad1cf83281a4c1231fed5a71dd7a13b7c80d..a831d2e73a772ae6324dd82d3f31392ae427a42b 100644
--- a/webrtc/sdk/android/api/org/webrtc/AudioSource.java
+++ b/webrtc/sdk/android/api/org/webrtc/AudioSource.java
@@ -15,7 +15,19 @@ package org.webrtc;
  * more {@code AudioTrack} objects.
  */
 public class AudioSource extends MediaSource {
+  final long nativeSource;
+
   public AudioSource(long nativeSource) {
     super(nativeSource);
+    this.nativeSource = nativeSource;
+  }
+
+  /** Sets the volume for the MediaSource. volume is a gain value in the range
+   * 0 to 1
+   */
+  public void setVolume(double volume) {
+    nativeSetVolume(nativeSource, volume);
   }
+
+  private static native void nativeSetVolume(long nativeSource, double volume);
 }