Followup from bug 33821: there's no point in going into compositing mode for a 0x0 plugin
<rdar://problem/7935757>
This isn't as simple as it would appear to be, because we can't look at the renderer size from updateStyle() (where we make compositing decisions), because layout hasn't happened yet.
Created attachment 60843 [details] WIP patch
Sites to test: gmail.com Mobile Me "Find my iPhone" yahoo mail
Created attachment 61294 [details] Patch
I filed bug 42120 to optimize m_compositingDependsOnGeometry.
http://trac.webkit.org/changeset/63149