Throw IllegalStateException if native objects are used after dispose.

This makes it easier to debug issues related to double dispose /
use after dispose.

Bug: webrtc:7566, webrtc:8297
Change-Id: I07429b2b794deabb62b5f3ea1cf92eea6f66a149
Reviewed-on: https://webrtc-review.googlesource.com/102540
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Paulina Hensman <phensman@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24894}

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

@@ -20,7 +20,12 @@ public class AudioTrack extends MediaStreamTrack {
    *  0 to 10.
    */
   public void setVolume(double volume) {
-    nativeSetVolume(super.nativeTrack, volume);
+    nativeSetVolume(getNativeAudioTrack(), volume);
+  }
+
+  /** Returns a pointer to webrtc::AudioTrackInterface. */
+  long getNativeAudioTrack() {
+    return getNativeMediaStreamTrack();
   }
 
   private static native void nativeSetVolume(long track, double volume);