Bug 1637459 - Make nsXULElement::HasMenu flush frames. r=tnikkel

The UITour code assumes that it will return the up-to-date value, which
doesn't happen with lazy frame construction.

This is used sparingly in the front end code, so it doesn't quite
warrant more optimization.

Differential Revision: https://phabricator.services.mozilla.com/D75710

dom/xul/nsXULElement.cpp

@@ -429,8 +429,8 @@ int32_t nsXULElement::ScreenY() {
 }
 
 bool nsXULElement::HasMenu() {
-  nsMenuFrame* menu = do_QueryFrame(GetPrimaryFrame());
-  return menu != nullptr;
+  nsMenuFrame* menu = do_QueryFrame(GetPrimaryFrame(FlushType::Frames));
+  return !!menu;
 }
 
 void nsXULElement::OpenMenu(bool aOpenFlag) {

dom/xul/nsXULElement.h

@@ -340,7 +340,7 @@ class nsXULElement : public nsStyledElement {
   MOZ_CAN_RUN_SCRIPT int32_t ScreenX();
   MOZ_CAN_RUN_SCRIPT int32_t ScreenY();
 
-  bool HasMenu();
+  MOZ_CAN_RUN_SCRIPT bool HasMenu();
   MOZ_CAN_RUN_SCRIPT void OpenMenu(bool aOpenFlag);
 
   virtual bool PerformAccesskey(bool aKeyCausesActivation,