With site-per-process enabled a spare renderer process will be created
for use with a future browser or navigation. Consequently the
|extra_info| parameter populated in OnRenderProcessThreadCreated will no
longer be delivered to OnRenderThreadCreated in the expected renderer
process. To avoid confusion these callbacks have been removed completely.
After this change CefRenderProcessHandler::OnWebKitInitialized should
be used for startup tasks in the render process, and OnBrowserCreated
should be used in the render process to recieve |extra_info| passed from
CefBrowserHost::CreateBrowser or CefLifeSpanHandler::OnBeforePopup.