We need to update the occlusion state when the page goes back into the window.
Created attachment 205739 [details] Fix
Fixed in r152187
Landed - https://github.com/WebKit/WebKit/commit/db015854c91de73c3e0aae0ba4da5cd8d18fc5f0 and didn't backed out (while checking with BugID on Webkit). Marking this as "RESOLVED FIXED".