Build cast_unittest

Build cast targets on all bots.

R=justinlin@chromium.org

Review URL: https://codereview.chromium.org/25891004

git-svn-id: http://src.chromium.org/svn/trunk/src/build@226914 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

all.gyp

@@ -41,6 +41,7 @@
             '../gpu/tools/tools.gyp:*',
             '../ipc/ipc.gyp:*',
             '../jingle/jingle.gyp:*',
+            '../media/cast/cast.gyp:*',
             '../media/media.gyp:*',
             '../ppapi/ppapi.gyp:*',
             '../ppapi/ppapi_internal.gyp:*',