Fix/suppress all javac warnings.

This is done in preparation to make all javac warnings into errors for
WebRTC targets.

Bug: webrtc:6597
Change-Id: I402043157bd75943adf0de52111e5a1bb179c6d1
Reviewed-on: https://webrtc-review.googlesource.com/15104
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20450}

examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java

@@ -725,6 +725,7 @@ public class PeerConnectionClient {
     return rootEglBase.getEglBaseContext();
   }
 
+  @SuppressWarnings("deprecation") // TODO(sakal): getStats is deprecated.
   private void getStats() {
     if (peerConnection == null || isError) {
       return;