Remove lots of noop work from StyleResolverState

1% of squished presidents recalcStyle is in creating StyleResolverState.
Looking at it the class does lots of stuff that's not neccesary, and
the entire destructor is also wasted work.

Long ago we used StyleResolverState multiple times per resolve and needed
to call clear() each time. Now we store it on the stack and never reuse it
so we don't need all this cleanup logic or clear() methods.

Review URL: https://codereview.chromium.org/26914005

git-svn-id: svn://svn.chromium.org/blink/trunk@159524 bbb929c8-8fbe-4397-9dbb-9b2b20218538