Convert MdSettingsUI to use the new navigation callbacks.

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 3f1d929bca97bea2f86ae66bcc6dcae30ac2f020..f09d09efd2eedcb9a4b9eba51ce2b75399796b51 100644
--- a/chrome/browser/ui/webui/settings/md_settings_ui.h
+++ b/chrome/browser/ui/webui/settings/md_settings_ui.h
@@ -26,10 +26,8 @@ class MdSettingsUI : public content::WebUIController,
   ~MdSettingsUI() override;
 
   // content::WebContentsObserver:
-  void DidStartProvisionalLoadForFrame(
-      content::RenderFrameHost* render_frame_host,
-      const GURL& validated_url,
-      bool is_error_page) override;
+  void DidStartNavigation(
+      content::NavigationHandle* navigation_handle) override;
   void DocumentLoadedInFrame(
       content::RenderFrameHost *render_frame_host) override;
   void DocumentOnLoadCompletedInMainFrame() override;