Revert 159884 "Devirtualize type checks in RenderObject."

This didn't provide the performance improvement to warrent the code complexity.

> 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

TBR=dsinclair@chromium.org

Review URL: https://codereview.chromium.org/30693002

git-svn-id: svn://svn.chromium.org/blink/trunk@160016 bbb929c8-8fbe-4397-9dbb-9b2b20218538