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/RtpReceiver.java

@@ -22,7 +22,7 @@ public class RtpReceiver {
     public void onFirstPacketReceived(MediaStreamTrack.MediaType media_type);
   }
 
-  final long nativeRtpReceiver;
+  private long nativeRtpReceiver;
   private long nativeObserver;
 
   @Nullable private MediaStreamTrack cachedTrack;
@@ -40,28 +40,34 @@ public class RtpReceiver {
   }
 
   public boolean setParameters(@Nullable RtpParameters parameters) {
+    checkRtpReceiverExists();
     return parameters == null ? false : nativeSetParameters(nativeRtpReceiver, parameters);
   }
 
   public RtpParameters getParameters() {
+    checkRtpReceiverExists();
     return nativeGetParameters(nativeRtpReceiver);
   }
 
   public String id() {
+    checkRtpReceiverExists();
     return nativeGetId(nativeRtpReceiver);
   }
 
   @CalledByNative
   public void dispose() {
+    checkRtpReceiverExists();
     cachedTrack.dispose();
     if (nativeObserver != 0) {
       nativeUnsetObserver(nativeRtpReceiver, nativeObserver);
       nativeObserver = 0;
     }
     JniCommon.nativeReleaseRef(nativeRtpReceiver);
+    nativeRtpReceiver = 0;
   }
 
   public void SetObserver(Observer observer) {
+    checkRtpReceiverExists();
     // Unset the existing one before setting a new one.
     if (nativeObserver != 0) {
       nativeUnsetObserver(nativeRtpReceiver, nativeObserver);
@@ -70,9 +76,16 @@ public class RtpReceiver {
   }
 
   public void setFrameDecryptor(FrameDecryptor frameDecryptor) {
+    checkRtpReceiverExists();
     nativeSetFrameDecryptor(nativeRtpReceiver, frameDecryptor.getNativeFrameDecryptor());
   }
 
+  private void checkRtpReceiverExists() {
+    if (nativeRtpReceiver == 0) {
+      throw new IllegalStateException("RtpReceiver has been disposed.");
+    }
+  }
+
   // This should increment the reference count of the track.
   // Will be released in dispose().
   private static native long nativeGetTrack(long rtpReceiver);