Add some sanity CHECKs to webrtc::Call.

These checks would help catching double-deletes, forgetting to destroy
streams and also catch if VideoEngine has held on to any stale
references.

BUG=1788
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/42929004

Cr-Commit-Position: refs/heads/master@{#8866}
1 file changed