Remove viewport rule special casing from StyleResolver.

As best I can tell, this was only needed because the tests didn't
correctly force a style recalc before measuring viewport sizes.
The tests used to synchronously update the stylesheets when they
were modified, with r162187 they do so at recalc time.

The tests in question are the css3/device-adapt tests.
Now have the Internals API force a recalc and update.

BUG=308796

Review URL: https://codereview.chromium.org/76623003

git-svn-id: svn://svn.chromium.org/blink/trunk@162411 bbb929c8-8fbe-4397-9dbb-9b2b20218538