Add support for loading extensions (issue #1947)

- 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.

tests/shared/browser/resource_util.h

@@ -30,15 +30,10 @@ CefRefPtr<CefStreamReader> GetBinaryResourceReader(const char* resource_name);
 #if defined(OS_WIN)
 // Create a new provider for loading binary resources.
 CefResourceManager::Provider* CreateBinaryResourceProvider(
-    const std::string& url_path);
+    const std::string& url_path,
+    const std::string& resource_path_prefix);
 #endif
 
-// Load an image icon at different scale factors. The image representations are
-// expected to be 16 DIP in size. For example, if |icon_name| is "image" then
-// the expected file names are "image.1x.png" for the 1x scale image (16 pixels)
-// and "image.2x.png" for the 2x scale image (32 pixels).
-CefRefPtr<CefImage> LoadImageIcon(const char* icon_name);
-
 }  // namespace client
 
 #endif  // CEF_TESTS_SHARED_BROWSER_RESOURCE_UTIL_H_