Converted dojo/window viewport dimension tests to intern.

The dojo/window tests are going to be tough to convert. I would like some feedback before proceeding with conversion of all the dojo/window doh tests. 

I did the conversion with as a little change to the original doh tests as possible. 

Here is a link to the original tests for comparison. https://github.com/dojo/dojo/blob/master/tests/window/viewport.html