Devirtualize type checks in RenderObject.

This adds two flags into RenderObject, one for the base objects and one for the
objects marked FINAL. For any of the FINAL types they are mutually exclusive,
for the base types, you can have a bunch of them set at the same time

BUG=271114,302830

Review URL: https://codereview.chromium.org/26302005

git-svn-id: svn://svn.chromium.org/blink/trunk@159884 bbb929c8-8fbe-4397-9dbb-9b2b20218538