Allow direct communication between a helper process and the renderer.

Some raw ideas

• what if Electron would provide an API similar to BrowserWindow.loadUrl but UtilityProcess.loadUrl to create such a child process
• Electron should delegate this to Chrome and reuse the ability Chrome has to spawn utility processes like GPU and Network
• Utility process has node.js integration enabled and direct communication support to a renderer (either via electron IPC or message ports)