Fix perf regression on vnexpress.net.

The regression is from http://src.chromium.org/viewvc/blink?revision=162662&view=revision.
The problem was that we were throwing away the StyleResolver
if there was a forced pending recalc. Instead, early return
after the compareStyleSheets call, but before the expensive
StyleInvalidationAnalysis.

BUG=324908

Review URL: https://codereview.chromium.org/100113002

git-svn-id: svn://svn.chromium.org/blink/trunk@163100 bbb929c8-8fbe-4397-9dbb-9b2b20218538