Add more sanity checks to workaround the unidentified problem that CaptureThread is still running while related resouces are destroyed already.

BUG=
TEST=auto test
R=henrika@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/28859004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7590 4adac7df-926f-26a2-2b94-8c16560cd09d