Fix multi-monitor support in the screen capturer for Mac.

This feature was broken in r5471.

BUG=361919
R=jiayl@webrtc.org

Committed: https://code.google.com/p/webrtc/source/detail?r=5937

Review URL: https://webrtc-codereview.appspot.com/12109004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5942 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed