Add check to help prevent test-only function usage in production code.
Add check to help prevent test-only function usage in production code.

BUG=none
TEST=Manual testing was performed. Warning message from presubmit test includes note to report issues to joi@chromium.org

Review URL: http://codereview.chromium.org/7582002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@96184 0039d316-1c4b-4281-b951-d872f2087c98

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