Add initial WebUI support (issue #2037)

- Visit chrome://webui-hosts for the list of supported hosts.

patch/patch.cfg

@@ -274,4 +274,12 @@ patches = [
     'name': 'webview_plugin_2020',
     'path': '../',
   },
+  {
+    # Support WebUI by:
+    # (a) Exposing required UserData keys;
+    # (b) Removing dependency on non-NULL IOThread* object.
+    # https://bitbucket.org/chromiumembedded/cef/issues/2037
+    'name': 'webui_2037',
+    'path': '../',
+  },
 ]