Revert 7625 "Don't use DCHECK when you need the side effects..."

Reverting since 7623 might depend on this one

> Don't use DCHECK when you need the side effects...
> 
> R=pbos@webrtc.org
> TBR=henrik.lundin@webrtc.org
> 
> Review URL: https://webrtc-codereview.appspot.com/32369004

TBR=kwiberg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/25089004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7628 4adac7df-926f-26a2-2b94-8c16560cd09d