Ensure WEBRTC_MODULE_UTILITY_VIDEO is undefined for enable_video==0.

Move the logic to common.gypi to reduce the chance of the define being
unprotected in the future.

BUG=b/12018143
TESTED=git try, and local Linux build with -Denable_video=0
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/5309004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5244 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed