Bug 1959023 Part 2: Prevent macOS menubar from flickering when quitting Firefox. r=spohl a=RyanVM

This also prevents the momentary appearance of a gray, disabled-looking
menubar when quitting.

Differential Revision: https://phabricator.services.mozilla.com/D255244

toolkit/components/startup/nsAppStartup.cpp

@@ -621,6 +621,12 @@ nsAppStartup::GetShuttingDown(bool* aResult) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsAppStartup::GetAttemptingQuit(bool* aResult) {
+  *aResult = mAttemptingQuit;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsAppStartup::GetStartingUp(bool* aResult) {
   *aResult = mStartingUp;

toolkit/components/startup/public/nsIAppStartup.idl

@@ -202,6 +202,13 @@ interface nsIAppStartup : nsISupports
      */
     [infallible] readonly attribute boolean shuttingDown;
 
+    /**
+     * True if the application is attempting to quit (Quit has been called). This
+     * is an early signal that we are headed to shutdown. It becomes true just
+     * before we start closing windows.
+     */
+    [infallible] readonly attribute boolean attemptingQuit;
+
     /**
      * True if the application is in the process of starting up.
      *

widget/cocoa/nsCocoaWindow.mm

@@ -8,12 +8,14 @@
 
 #include "nsArrayUtils.h"
 #include "nsCursorManager.h"
+#include "nsIAppStartup.h"
 #include "nsIDOMWindowUtils.h"
 #include "nsILocalFileMac.h"
 #include "GLContextCGL.h"
 #include "MacThemeGeometryType.h"
 #include "NativeMenuSupport.h"
 #include "WindowRenderer.h"
+#include "mozilla/Components.h"
 #include "mozilla/MiscEvents.h"
 #include "mozilla/SwipeTracker.h"
 #include "mozilla/layers/APZInputBridge.h"
@@ -7109,9 +7111,17 @@ void nsCocoaWindow::CocoaWindowDidResize() {
   RefPtr<nsMenuBarX> hiddenWindowMenuBar =
       nsMenuUtilsX::GetHiddenWindowMenuBar();
   if (hiddenWindowMenuBar) {
-    // We do an async paint in order to prevent crashes when macOS is actively
-    // enumerating the menu items in `NSApp.mainMenu`.
-    hiddenWindowMenuBar->PaintAsyncIfNeeded();
+    bool isTerminating = false;
+    nsCOMPtr<nsIAppStartup> appStartup(components::AppStartup::Service());
+    if (appStartup) {
+      appStartup->GetAttemptingQuit(&isTerminating);
+    }
+
+    if (!isTerminating) {
+      // We do an async paint in order to prevent crashes when macOS is actively
+      // enumerating the menu items in `NSApp.mainMenu`.
+      hiddenWindowMenuBar->PaintAsyncIfNeeded();
+    }
   }
 
   NSWindow* window = [aNotification object];