AppRTCDemo.java: unbreak build following addition of PeerConnection.Observer.onDataChannel()
Also fixed gyp to unhide future breakages.

BUG=https://code.google.com/p/webrtc/issues/detail?id=2048
RISK=P3
TESTED=AppRTCDemo builds in a clean checkout, and adding an unimplented new interface method to PeerConnection.Observer now breaks the build, correctly.
R=braveyao@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1776006

git-svn-id: http://libjingle.googlecode.com/svn/trunk@366 dd674b97-3498-5ee5-1854-bdd07cd0ff33
2 files changed