Fix for functional regressions of JDK-8151756 + add a sytem test

Author: aghaisas

modules/javafx.graphics/src/main/java/javafx/scene/Node.java

@@ -1184,8 +1184,10 @@ public final ReadOnlyObjectProperty<Scene> sceneProperty() {
      * Exists for Parent and LightBase
      */
     void scenesChanged(final Scene newScene, final SubScene newSubScene,
-                       final Scene oldScene, final SubScene oldSubScene) { }
-
+                       final Scene oldScene, final SubScene oldSubScene) {
+        // On scenes change, reapply CSS for this Node
+        reapplyCSS();
+    }
 
     /**
      * The id of this {@code Node}. This simple string identifier is useful for

modules/javafx.graphics/src/main/java/javafx/scene/Parent.java

@@ -756,6 +756,7 @@ final void toBack(Node node) {
     @Override
     void scenesChanged(final Scene newScene, final SubScene newSubScene,
                        final Scene oldScene, final SubScene oldSubScene) {
+        super.scenesChanged(newScene, newSubScene, oldScene, oldSubScene);
 
         if (oldScene != null && newScene == null) {
             // RT-34863 - clean up CSS cache when Parent is removed from scene-graph

tests/system/src/test/java/test/robot/javafx/scene/CSSPerf_JDK8193445Test.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2019, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package test.robot.javafx.scene;
+
+import javafx.geometry.Insets;
+import javafx.scene.Scene;
+import javafx.scene.layout.HBox;
+import javafx.scene.layout.BorderPane;
+import javafx.scene.text.Text;
+import javafx.stage.Stage;
+
+import org.junit.Test;
+import test.robot.testharness.VisualTestBase;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * This test is based on the test case reported in JDK-8209830
+ *
+ * Redundant CSS Re-application was avoided in JDK-8193445.
+ * It results in faster application of CSS on Controls (Nodes). In turn,
+ * resulting in improved Node creation/addition time to a Scene.
+ *
+ * The goal of this test is *NOT* to measure absolute performance, but to show
+ * creating and adding 300 Nodes to a scene does not take more than a
+ * particular threshold of time.
+ *
+ * The selected thresold is larger than actual observed time.
+ * It is not a benchmark value. It is good enough to catch the regression
+ * in performance, if any.
+ */
+
+public class CSSPerf_JDK8193445Test extends VisualTestBase {
+
+    private Stage testStage;
+    private Scene testScene;
+    private BorderPane pane = new BorderPane();
+    private long mSec = 0;
+
+    @Test(timeout = 15000)
+    public void testTimeForAdding300NodesToScene() {
+        runAndWait(() -> {
+            testStage = getStage();
+            testScene = new Scene(pane);
+            testStage.setScene(testScene);
+            testStage.show();
+        });
+
+        waitFirstFrame();
+
+        // Measure time to create and add 300 Nodes to Scene
+        runAndWait(() -> {
+            long startTime = System.currentTimeMillis();
+
+            HBox hbox = new HBox();
+            for (int i = 0; i < 300; i++) {
+                hbox = new HBox(new Text("y"), hbox);
+                final HBox h = hbox;
+                h.setPadding(new Insets(1));
+            }
+            pane.setCenter(hbox);
+
+            long endTime = System.currentTimeMillis();
+
+            mSec = endTime - startTime;
+        });
+
+        System.out.println("Time to create and add 300 nodes to a Scene = " + mSec + " mSec");
+
+        // NOTE : 400 mSec is not a benchmark value
+        // It is good enough to catch the regression in performance, if any
+        assertTrue("Time to add 300 Nodes is more than 400 mSec", mSec < 400);
+    }
+}