Windows: Add off-screen rendering support (issue #518).

- Popup menus, drag&drop and GPU acceleration are not currently supported.
- Testing is enabled in cefclient by passing the "off-screen-rendering-enabled" command-line flag.

git-svn-id: https://chromiumembedded.googlecode.com/svn/trunk@919 5089003a-bbd8-11dd-ad1f-f1f9622dbc98

include/cef_client.h

@@ -50,6 +50,7 @@
 #include "include/cef_life_span_handler.h"
 #include "include/cef_load_handler.h"
 #include "include/cef_process_message.h"
+#include "include/cef_render_handler.h"
 #include "include/cef_request_handler.h"
 
 ///
@@ -143,6 +144,14 @@ class CefClient : public virtual CefBase {
     return NULL;
   }
 
+  ///
+  // Return the handler for off-screen rendering events.
+  ///
+  /*--cef()--*/
+  virtual CefRefPtr<CefRenderHandler> GetRenderHandler() {
+    return NULL;
+  }
+
   ///
   // Return the handler for browser request events.
   ///