8273355: Flickering on tooltip appearance IntelliJ IDEA 2021.2.1

Reviewed-by: serb, aghaisas

Author: Alexey Ushakov

src/java.desktop/macosx/classes/sun/lwawt/LWWindowPeer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -59,6 +59,7 @@
 import java.awt.peer.WindowPeer;
 import java.util.List;
 
+import java.util.Objects;
 import javax.swing.JComponent;
 
 import sun.awt.AWTAccessor;
@@ -281,6 +282,16 @@ protected void disposeImpl() {
         super.disposeImpl();
     }
 
+    @Override
+    public void setBackground(final Color c) {
+        Color oldBg = getBackground();
+        if (Objects.equals(oldBg, c)) {
+            return;
+        }
+        super.setBackground(c);
+        updateOpaque();
+    }
+
     @Override
     protected void setVisibleImpl(final boolean visible) {
         if (!visible && warningWindow != null) {