Got rid of ContentsWidth and ContentsHeight, which seems hard (or at least non-obvious) to support w/ CEF3 and I don't really see why we need it in the first place. "Less software". :)
Let IRenderWebBrowser expose its width and height to the RenderClientAdapterInternal class, so we can let Chromium render in a bitmap of the right size.
Let's scrap these also, at least for the time being. Supporting them with CEF3 is semi-problematic, so let's remove them and then we can add them back if they are really needed (and we manage to figure out how to support it with CEF3).
Silly bug: ActualWidth and ActualHeight wasn't really distinguished between properly...
Added support for resizing. Doesn't work fully, throws exceptions sometimes, but it's at least a start.
Made the exposure of CefBrowserHost more generic, since we will use it for many other use cases shortly.