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/capi/cef_display_handler_capi.h

@@ -80,7 +80,8 @@ typedef struct _cef_display_handler_t {
   // text that will be displayed in the tooltip. To handle the display of the
   // tooltip yourself return true (1). Otherwise, you can optionally modify
   // |text| and then return false (0) to allow the browser to display the
-  // tooltip.
+  // tooltip. When window rendering is disabled the application is responsible
+  // for drawing tooltips and the return value is ignored.
   ///
   int (CEF_CALLBACK *on_tooltip)(struct _cef_display_handler_t* self,
       struct _cef_browser_t* browser, cef_string_t* text);