Test chrome

@ussuri Since chrome 31 is release - and that's our min. dependency - I thought it'd make sense to try and get the tests running on chrome again. It looks like drone.io has not yet upgraded to chrome 31 however. In any case, here is a CL which cleans up our chrome testing story. There are 3 failures under dart2js, that don't fail under Dartium, that we'll have to investigate.