Fix m_needsToUpdateAncestorDependentProperties ASSERT

In certain scrolling modes, we can trigger the ASSERT guarding the
RenderLayer::ancestorDependentProperties because we dirty the
ancestorDependentProperties when the visibility of a RenderLayer, but we defer
computing whether the visibility has changed until we compute the
decendant-dependant properties.

This CL adds a call to updateDescendantDependentFlags in
CompositingPropertyUpdater to ensure that these properties are clean before
cleaning the AncestorDependentProperties.

R=vollick@chromium.org
BUG=362753

Review URL: https://codereview.chromium.org/236303009

git-svn-id: svn://svn.chromium.org/blink/trunk@171514 bbb929c8-8fbe-4397-9dbb-9b2b20218538