disable broken test until fixing is possible

I don't know a way to make this test work after issue 20143 was "fixed" 
because I'm not able to use the `resizeTo` method anymore. 
Maybe issue 20216 leads to a solution.
Thanks for the feedback. 
Being consistent in these matters is pretty difficult ;-)
My attempt was (as I did when porting polymer-(ui-)elements) to check the diff between polymer-elements JS repo when I did the last update and the current state of the JS repo to show what changes were made and integrated those changes into the Dart port. I didn't expect a diff between the JS source and the ported Dart source to be very expressive.