Move gtest/gmock BUILD.gn files to main tree.

Also moves the "unused variable warning" to a config in the build directory so
it can be shared with outher targets without duplication on the command line.

BUG=
R=cjhopman@chromium.org

Review URL: https://codereview.chromium.org/219433005

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@260949 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
Revert 260949 "Move gtest/gmock BUILD.gn files to main tree."

> Move gtest/gmock BUILD.gn files to main tree.
> 
> Also moves the "unused variable warning" to a config in the build directory so
> it can be shared with outher targets without duplication on the command line.
> 
> BUG=
> R=cjhopman@chromium.org
> 
> Review URL: https://codereview.chromium.org/219433005

TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/218493017

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@260954 4ff67af0-8c30-449e-8e8b-ad334ec8d88c