MD Settings: About page, add an explicit 'aboutPageReady' signal.

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

Index: chrome/browser/ui/webui/settings/about_handler.h
diff --git a/chrome/browser/ui/webui/settings/about_handler.h b/chrome/browser/ui/webui/settings/about_handler.h
index 7477cd11e8a3a28edd87604de5ef91d97ddcf7cf..b5b3df1ea2dbafe6569351063372161eda8ddfea 100644
--- a/chrome/browser/ui/webui/settings/about_handler.h
+++ b/chrome/browser/ui/webui/settings/about_handler.h
@@ -66,6 +66,10 @@ class AboutHandler : public settings::SettingsPageUIHandler,
   void OnDeviceAutoUpdatePolicyChanged(const base::Value* previous_policy,
                                        const base::Value* current_policy);
 
+  // Called once the JS page is ready to be called, serves as a signal to the
+  // handler to register C++ observers.
+  void HandlePageReady(const base::ListValue* args);
+
   // Called once when the page has loaded. On ChromeOS, this gets the current
   // update status. On other platforms, it will request and perform an update
   // (if one is available).