Enables early out on trybot mac_chromium_rel

BUG=383609
TEST=none
TBR=iannucci@chromium.org

Review URL: https://codereview.chromium.org/411543002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284700 0039d316-1c4b-4281-b951-d872f2087c98

testing/buildbot/chromium_trybot.json

@@ -191,6 +191,7 @@
   ],
 
   "filter_builders": [
-    "linux_chromium_clang_dbg"
+    "linux_chromium_clang_dbg",
+    "mac_chromium_rel"
   ]
 }