Invalidate paint when layout an RenderSliderContainer object.

This is necessary because this class uses one-off code that does not go through the regular style/layout system.

BUG=392694

Review URL: https://codereview.chromium.org/418643003

git-svn-id: svn://svn.chromium.org/blink/trunk@178883 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL: Introduce IdlTypeBase

IdlType and IdlUnionType have similar structures, so it might be good to have
the common superclass.

BUG=345503

Review URL: https://codereview.chromium.org/410103002

git-svn-id: svn://svn.chromium.org/blink/trunk@178884 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Drop slower Node::hasID() / Node::hasClass() methods

Drop slower Node::hasID() / Node::hasClass() methods. Those were here for
convenience but there are very few remaining callers as we use tighter
typing in the code these days. Removing them will encourage future callers
to use tighter typing and call the methods on Element.

This CL updates the 2 remaining call sites to use the methods on Element
instead.

R=abarth@chromium.org, eseidel@chromium.org

Review URL: https://codereview.chromium.org/415243003

git-svn-id: svn://svn.chromium.org/blink/trunk@178885 bbb929c8-8fbe-4397-9dbb-9b2b20218538