Style changes shouldn't cause RenderLayerCompositor to rebuild its tree

Before this CL, if you changed the style on a RenderLayer that was directly
composited, we would trigger a rebuild of the entire compositing tree as part
of the "chicken-egg hacks." There's no reason for that. Instead, we simply need
to do a geometry update after changing style.

This makes the compositing update in the calculator faster by 7%.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/220193003

git-svn-id: svn://svn.chromium.org/blink/trunk@170515 bbb929c8-8fbe-4397-9dbb-9b2b20218538