Make AppRTCDemoTest pass without Internet connection.

The AppRTCDemoTest is failing if the Android device lacks
an Internet connection (e.g. is in flight mode).
This change makes it benefit from the work done in
https://review.webrtc.org/36769004/ to work around that
limitation for loopback tests.

R=phoglund@webrtc.org
TBR=glaznev@webrtc.org
BUG=4421
TESTED=Successful run on Nexus 7 (2013) in flight mode using:
ninja -C out/Release
. build/android/envsetup.sh
adb install -r out/Release/apks/AppRTCDemo.apk
webrtc/build/android/test_runner.py instrumentation --test-apk AppRTCDemoTest --verbose --release

Review URL: https://webrtc-codereview.appspot.com/45649004

Cr-Commit-Position: refs/heads/master@{#8714}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8714 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/examples/android/src/org/appspot/apprtc/PeerConnectionClient.java

@@ -330,9 +330,16 @@ public class PeerConnectionClient {
       events.onPeerConnectionError("Failed to initializeAndroidGlobals");
     }
     factory = new PeerConnectionFactory();
+    configureFactory(factory);
     Log.d(TAG, "Peer connection factory created.");
   }
 
+  /**
+   * Hook where tests can provide additional configuration for the factory.
+   */
+  protected void configureFactory(PeerConnectionFactory factory) {
+  }
+
   private void createPeerConnectionInternal() {
     if (factory == null || isError) {
       Log.e(TAG, "Peerconnection factory is not created");