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

webrtc/sdk/android/src/jni/peerconnection_jni.cc

Index: webrtc/sdk/android/src/jni/peerconnection_jni.cc
diff --git a/webrtc/sdk/android/src/jni/peerconnection_jni.cc b/webrtc/sdk/android/src/jni/peerconnection_jni.cc
index 75b1bad20256dcafd288b6a953d8e686c8a216ca..10d3469d65f554cec20082bd958ff8efe0c9f209 100644
--- a/webrtc/sdk/android/src/jni/peerconnection_jni.cc
+++ b/webrtc/sdk/android/src/jni/peerconnection_jni.cc
@@ -1199,6 +1199,13 @@ JOW(void, PeerConnectionFactory_shutdownInternalTracer)(JNIEnv* jni, jclass) {
   rtc::tracing::ShutdownInternalTracer();
 }
 
+JOW(void, AudioTrack_nativeSetVolume)
+(JNIEnv*, jclass, jlong j_p, jdouble volume) {
+  rtc::scoped_refptr<AudioSourceInterface> source(
+      reinterpret_cast<AudioTrackInterface*>(j_p)->GetSource());
+  source->SetVolume(volume);
+}
+
 // Helper struct for working around the fact that CreatePeerConnectionFactory()
 // comes in two flavors: either entirely automagical (constructing its own
 // threads and deleting them on teardown, but no external codec factory support)