Hook up LayerTypeCustom with the remote layer tree so that video and plugins and other things which are difficult, dangerous, or impossible to serialize can live in the Web (or eventually other) process, with their own little miniature CALayer tree, hosted in a CALayerHost in the UI process. This should make video and plugins work (and it should be trivial to make things like PDFPlugin work on top, but in a different patch), though plugins will need later additional cleanup to avoid double-hosting (plugin process->web process->ui process).
Created attachment 215983 [details] patch
Created attachment 215984 [details] patch
http://trac.webkit.org/changeset/158647