Add CHECK to EventWrapper to see if there's a subtle bug there or not.
Add CHECK to EventWrapper to see if there's a subtle bug there or not.

R=pbos@webrtc.org
BUG=

Review URL: https://webrtc-codereview.appspot.com/38039005

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@8302 4adac7df-926f-26a2-2b94-8c16560cd09d

svn2github/webrtc-Revision-8758,svn2github/webrtc-Revision-8758,svn2github/webrtc-Revision-8758,svn2github/webrtc-Revision-8758,svn2github/webrtc-Revision-8758,svn2github/webrtc-Revision-8758