JBR-2019 provide getWindowHandle method for jcef

(cherry picked from commit 7ae706b629)

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

@@ -79,6 +79,7 @@ import sun.java2d.SurfaceData;
 import sun.java2d.loops.Blit;
 import sun.java2d.loops.CompositeType;
 import sun.java2d.pipe.Region;
+import sun.lwawt.macosx.CPlatformWindow;
 import sun.util.logging.PlatformLogger;
 
 public class LWWindowPeer
@@ -1523,4 +1524,17 @@ public class LWWindowPeer
     public String toString() {
         return super.toString() + " [target is " + getTarget() + "]";
     }
+
+    /**
+     * [tav] Used externally.
+     */
+    @Override
+    public long getWindowHandle() {
+        final long[] handle = new long[1];
+        PlatformWindow window = getPlatformWindow();
+        if (window instanceof CPlatformWindow) {
+            ((CPlatformWindow)window).execute(ptr -> handle[0] = ptr);
+        }
+        return handle[0];
+    }
 }

src/java.desktop/share/classes/java/awt/peer/WindowPeer.java

@@ -126,6 +126,15 @@ public interface WindowPeer extends ContainerPeer {
      */
     default Insets getSysInsets() { return null; }
 
+    /**
+     * Returns platform window handle.
+     *
+     * @return the window handle
+     */
+    default long getWindowHandle() {
+        throw new UnsupportedOperationException("unimplemented");
+    }
+
     /**
      * Requests a GC that best suits this Window. The returned GC may differ
      * from the requested GC passed as the argument to this method. This method