This change moves the runtime-specific implementations of CefBrowserHostImpl
methods to CefBrowserPlatformDelegate. Some WebContentsDelegate methods
implemented by CefBrowserHostImpl set state or trigger client callbacks.
Those implementations will likely stay with CefBrowserHostImpl and will
need to be called from the Browser equivalents when using the Chrome runtime.
- Add CefRequestContext::LoadExtension, CefExtension, CefExtensionHandler and
related methods/interfaces.
- Add chrome://extensions-support that lists supported Chrome APIs.
- Add CefBrowserHost::SetAutoResizeEnabled and CefDisplayHandler::OnAutoResize
to support browser resize based on preferred web contents size.
- views: Add support for custom CefMenuButton popups.
- cefclient: Run with `--load-extension=set_page_color` command-line flag for
an extension loading example. Add `--use-views` on Windows and Linux for an
even better example.
