GN: Add common configs to tools and test.

Similar changes as in https://review.webrtc.org/28589004/
were missed in https://review.webrtc.org/25569004/.
This should fix the Chromium WebRTC FYI bots that currently
are broken due to lack of include paths.

BUG=3441
TBR=henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/25749004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7347 4adac7df-926f-26a2-2b94-8c16560cd09d