Should not use clipOutRoundedRect when a given rounded rect is empty.

BUG=303922,303383
TEST=fast/borders/border-radius-with-empty-inner-border.html,fast/borders/empty-border-radius.html

Review URL: https://codereview.chromium.org/25977004

git-svn-id: svn://svn.chromium.org/blink/trunk@159641 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove styleSharingCandidateMatchesRuleSet from StyleResolver

This code is only needed inside SharedStyleFinder and should be
moved there. I also removed the FIXME from the top of SharedStyleFinder,
the StyleResolver is needed in there for several reasons now.

This exposed that the "newStyle" argument to the SharedStyleFinder
is always null since we call it before doing setStyle() on the
StyleResolverState.

I also added an extra null check to m_style inside ElementRuleCollector.
I don't think we can ever get there if the m_style is null but it's not clear
and the one other user does check so we should for pseudo resolves
too.

Review URL: https://codereview.chromium.org/27281002

git-svn-id: svn://svn.chromium.org/blink/trunk@159642 bbb929c8-8fbe-4397-9dbb-9b2b20218538