There are various dynamic CSS and layout-related properties of an iframe element that need to be propagated to an out-of-process iframe for it to render properly. These currently include inertness, CSS visibility and viewport intersection rect. The list might expand over time.

A noteworthy part of these is that they need to survive cross-process navigations, so we cache them in the browser process (CrossProcessFrameConnector) and re-send them when the navigation is completed. Currently they are sent at the time the RenderWidgetHostImpl sends screen rects, but this might not be the best time (see comment in RenderWidgetHostViewChildFrame::WillSendScreenRects()). Also, it might make sense to consolidate these into a single ChildFrameParams struct so a new IPC doesn't need to be created every time we add an argument that matches this pattern.