In http://trac.webkit.org/changeset/160672, we unconditionally check m_properties.customAppearance in requiresCustomAppearanceUpdateOnBoundsChange without regard for whether it has ever been initialized. This would get us to send an uninitialized custom appearance to the UI process, which could end up requesting a shadow. I have a patch to initialize lots of things to their CA defaults.
Created attachment 219862 [details] patch
http://trac.webkit.org/changeset/161013