Simplify RenderObject::isRooted()

There's no reason to have the out param from this function, callers can
just use view() to get the RenderView in constant time. We can also
rewrite this function to walk the RenderLayer tree which should make it
faster, and by using isRootLayer() we can avoid the virtual call.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/215883003

git-svn-id: svn://svn.chromium.org/blink/trunk@171016 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add null element.animate method when API is switched off.

Having an empty element.animate method will act as a canary for potential breakages once the real element.animate is enabled. 

BUG=360469

Review URL: https://codereview.chromium.org/227393002

git-svn-id: svn://svn.chromium.org/blink/trunk@171017 bbb929c8-8fbe-4397-9dbb-9b2b20218538