MD Settings: Add helper method for responding to cr.sendWithPromise.

chrome/browser/ui/webui/settings/md_settings_ui.h

Index: chrome/browser/ui/webui/settings/md_settings_ui.h
diff --git a/chrome/browser/ui/webui/settings/md_settings_ui.h b/chrome/browser/ui/webui/settings/md_settings_ui.h
index 55cede3fd47142a28c8323c68dedea926f929f26..bdddd61f6ad9779645e0dcf62bc1406d6a4114e5 100644
--- a/chrome/browser/ui/webui/settings/md_settings_ui.h
+++ b/chrome/browser/ui/webui/settings/md_settings_ui.h
@@ -25,6 +25,12 @@ class SettingsPageUIHandler : public content::WebUIMessageHandler {
   // WebUIMessageHandler implementation.
   void RegisterMessages() override {}
 
+ protected:
+  // Helper method for responding to JS requests initiated with
+  // cr.sendWithPromise().
+  void CallJavascriptCallback(const base::Value& callback_id,
+                              const base::Value& response);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SettingsPageUIHandler);
 };