Inline RenderStyle functions for getting/setting pseudo style bits.

This is a merge of http://trac.webkit.org/changeset/158529 by
Andreas Kling <akling@apple.com>.

This patch inlines three hot functions in RenderStyle. This is
an 0.5% perf win on BlinkPerfMeasurement:Parser_html5-full-render.

Review URL: https://codereview.chromium.org/59233008

git-svn-id: svn://svn.chromium.org/blink/trunk@161425 bbb929c8-8fbe-4397-9dbb-9b2b20218538