Promote inlines to first-class invalidation citizens

Have RenderInline's update and invalidate themselves like other descendants of
RenderLayerModelObject by pulling most of the invalidation logic down into
RenderLayerModelObject.

We end up doing slightly more work, but we simplify multiple codepaths, which I believe is superior.

BUG=397455

Review URL: https://codereview.chromium.org/434453002

git-svn-id: svn://svn.chromium.org/blink/trunk@179682 bbb929c8-8fbe-4397-9dbb-9b2b20218538