RenderLayer::setNeedsCompositingInputsUpdate should schedule CompositingUpdateAfterCompositingInputChange

When we mark a RenderLayer as needing to update its compositing inputs, we
should schedule a CompositingUpdateAfterCompositingInputChange. Previously,
callers needed to do this manually, which was error-prone.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/343103002

git-svn-id: svn://svn.chromium.org/blink/trunk@176662 bbb929c8-8fbe-4397-9dbb-9b2b20218538