Try running MiniBrowser --bg-color="rgba(255,0,0,0)" -e for example, you should see the web view transparent, but what we get now is black wen view instead. This is because after r197062 we are now realizing the view too early, even before the toplevel window has been realized, forcing the toplevel window to be realized. If the RGBA visual is set on the window after it has been realzied it doesn't have any effect. We should wait until the toplevel window is realized to realize the web view, giving time to the application to set RGBA visual and background color.
Created attachment 273191 [details]
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See http://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Created attachment 273192 [details]
Fix coding style
Committed r197733: <http://trac.webkit.org/changeset/197733>