[Extension UI] Observing WebContentsObserver from extension_settings_handler.cc

chrome/browser/ui/webui/extensions/extension_settings_handler.cc

Index: chrome/browser/ui/webui/extensions/extension_settings_handler.cc
diff --git a/chrome/browser/ui/webui/extensions/extension_settings_handler.cc b/chrome/browser/ui/webui/extensions/extension_settings_handler.cc
index d6c017489136ee3732c56cc60240ee38454a62fe..5fdbfd24c8b7c04b2f49f4285b87a88698aa1cac 100644
--- a/chrome/browser/ui/webui/extensions/extension_settings_handler.cc
+++ b/chrome/browser/ui/webui/extensions/extension_settings_handler.cc
@@ -285,6 +285,8 @@ void ExtensionSettingsHandler::RegisterMessages() {
   // TODO(devlin): Take this out when everyone's been updated.
   Profile::FromWebUI(web_ui())->GetPrefs()->ClearPref(
       prefs::kExtensionsUIDismissedADTPromo);
+
+  content::WebContentsObserver::Observe(web_ui()->GetWebContents());
 }
 
 void ExtensionSettingsHandler::ReloadUnpackedExtensions() {