This (compile-time switchable) option automatically starts & stops calls in
series to stress-test the setup/teardown codepaths. When startCPULoad() is
removed (https://webrtc-codereview.appspot.com/972008/) this showed no
hangs/crashes after completing 200 start/stop pairs.
Also fixed a tiny shutdown-order bug (onDestroy() calling super.onDestroy()
before performing self-shutdown) and changed default video frame resolution to
640x480 to more effectively stress the device (and be a more compelling demo).
BUG=1162
Review URL: https://webrtc-codereview.appspot.com/939032
git-svn-id: http://webrtc.googlecode.com/svn/trunk@3238 4adac7df-926f-26a2-2b94-8c16560cd09d