Simplify WebRTC gatekeeper config.
Simplify WebRTC gatekeeper config.

Some renamed builders were currently not covered.
This change makes the config more robust against
such changes.

Review URL: https://codereview.chromium.org/1357893004

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@296842 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build