ServiceWorker unregister should not ASSERT on success.

The WebServiceWorkerProvider::unregisterServiceWorker interface
indicates the success callback accepts a WebServiceWorker. In
practice, unregister does not provide any value on success so Chrome
always passes NULL for this parameter. This wires Blink to commute
that NULL to 'undefined' for script, instead of ASSERTing
non-nullness.

Adds our first test for "unregister".

BUG=363851

Review URL: https://codereview.chromium.org/240323006

git-svn-id: svn://svn.chromium.org/blink/trunk@172100 bbb929c8-8fbe-4397-9dbb-9b2b20218538
compositing/overflow/iframe-scroll-children.html ASSERTs

The GraphicsLayerUpdater wasn't computing the compositingContainer correctly in
one corner case where the parent RenderLayer wasn't normal flow only. In that
case, the compositing ancestory comes from the stacking container, not just the
parent RenderLayer.

BUG=364991
NOTRY=true
R=vollick@chromium.org

Review URL: https://codereview.chromium.org/245053006

git-svn-id: svn://svn.chromium.org/blink/trunk@172101 bbb929c8-8fbe-4397-9dbb-9b2b20218538