Precompile out our standalone CHECK macros in a Chromium build.

As documented, the use of overrides/webrtc/base/logging.h in a Chromium
build reuslts in redefined macro errors. Fortunately, Chromium's macros
can be used as drop-in replacements for the standalone versions.

TBR=henrike

Review URL: https://webrtc-codereview.appspot.com/17239004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7004 4adac7df-926f-26a2-2b94-8c16560cd09d