rtc::CriticalSection: Add dummy implementation of IsLocked for release builds

In release mode, DCHECK still references the condition before throwing it away, so the function needs to be defined.

R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/50779004

Cr-Commit-Position: refs/heads/master@{#9070}
1 file changed