Merge updateVisibilityAfterStyleChange into RenderStyle::styleChanged

This function early outs, but it wasn't clear that it was doing that from
inside RenderLayer::styleChanged. Lets merge it back in since it's only
one line anyway and also add an ASSERT that the diff is >= repaint if the
visibility changed.

BUG=335703

Review URL: https://codereview.chromium.org/148963002

git-svn-id: svn://svn.chromium.org/blink/trunk@165963 bbb929c8-8fbe-4397-9dbb-9b2b20218538