8264950: Set opaque for JTooltip in config file of NimbusLookAndFeel

Reviewed-by: serb, pbansal

src/java.desktop/share/classes/javax/swing/plaf/nimbus/skin.laf

@@ -27248,7 +27248,7 @@
          <borderStates/>
          <regions/>
       </uiComponent>
-      <uiComponent opaque="false" type="javax.swing.JToolTip" name="ToolTip" ui="ToolTipUI" subregion="false">
+      <uiComponent opaque="true" type="javax.swing.JToolTip" name="ToolTip" ui="ToolTipUI" subregion="false">
          <stateTypes/>
          <contentMargins top="4" bottom="4" left="4" right="4"/>
          <style>

src/java.desktop/share/classes/javax/swing/plaf/synth/SynthToolTipUI.java

@@ -70,7 +70,6 @@ public class SynthToolTipUI extends BasicToolTipUI
     @Override
     protected void installDefaults(JComponent c) {
         updateStyle(c);
-        LookAndFeel.installProperty(c, "opaque", Boolean.TRUE);
     }
 
     private void updateStyle(JComponent c) {

test/jdk/javax/swing/JList/TestOpaqueListTable.java

@@ -33,7 +33,7 @@ import javax.swing.UnsupportedLookAndFeelException;
 
 /**
  *  @test
- *  @bug 8253266
+ *  @bug 8253266 8264950
  *  @summary setUIProperty should work when opaque property is not set by
  *  client
  *  @key headful