Needed to make it so changes containing only *.mm are only sent to Mac trybots by default.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/8059009

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@102930 0039d316-1c4b-4281-b951-d872f2087c98