7169111: Unreadable menu bar with Ambiance theme in GTK L&F

Reviewed-by: kizune

src/share/classes/com/sun/java/swing/plaf/gtk/GTKLookAndFeel.java

@@ -796,9 +796,10 @@ public class GTKLookAndFeel extends SynthLookAndFeel {
             "Menu.margin", zeroInsets,
             "Menu.cancelMode", "hideMenuTree",
             "Menu.alignAcceleratorText", Boolean.FALSE,
+            "Menu.useMenuBarForTopLevelMenus", Boolean.TRUE,
 
 
-            "MenuBar.windowBindings", new Object[] {
+                "MenuBar.windowBindings", new Object[] {
                 "F10", "takeFocus" },
             "MenuBar.font", new FontLazyValue(Region.MENU_BAR),
 

src/share/classes/com/sun/java/swing/plaf/gtk/GTKStyleFactory.java

@@ -92,7 +92,13 @@ class GTKStyleFactory extends SynthStyleFactory {
                 boolean defaultCapable = btn.isDefaultCapable();
                 key = new ComplexKey(wt, toolButton, defaultCapable);
             }
+        } else if (id == Region.MENU) {
+            if (c instanceof JMenu && ((JMenu) c).isTopLevelMenu() &&
+                    UIManager.getBoolean("Menu.useMenuBarForTopLevelMenus")) {
+                wt = WidgetType.MENU_BAR;
+            }
         }
+
         if (key == null) {
             // Otherwise, just use the WidgetType as the key.
             key = wt;

src/share/classes/javax/swing/plaf/synth/SynthMenuUI.java

@@ -299,7 +299,8 @@ public class SynthMenuUI extends BasicMenuUI
      */
     @Override
     public void propertyChange(PropertyChangeEvent e) {
-        if (SynthLookAndFeel.shouldUpdateStyle(e)) {
+        if (SynthLookAndFeel.shouldUpdateStyle(e) ||
+                (e.getPropertyName().equals("ancestor") && UIManager.getBoolean("Menu.useMenuBarForTopLevelMenus"))) {
             updateStyle((JMenu)e.getSource());
         }
     }