Disable failing browser tests for Linux

Contributes to
#1564

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_browser_Browser.java

@@ -845,6 +845,7 @@ public void test_OpenWindowListener_openHasValidEventDetails() {
 /** Test that a script 'window.open()' opens a child popup shell. */
 @Test
 public void test_OpenWindowListener_open_ChildPopup() {
+	assumeFalse("Not currently working on Linux, see https://github.com/eclipse-platform/eclipse.platform.swt/issues/1564", SwtTestUtil.isGTK);
 	AtomicBoolean childCompleted = new AtomicBoolean(false);
 
 	Shell childShell = new Shell(shell, SWT.None);
@@ -882,6 +883,8 @@ public void test_OpenWindowListener_open_ChildPopup() {
 /** Validate event order : Child's visibility should come before progress completed event */
 @Test
 public void test_OpenWindow_Progress_Listener_ValidateEventOrder() {
+	assumeFalse("Not currently working on Linux, see https://github.com/eclipse-platform/eclipse.platform.swt/issues/1564", SwtTestUtil.isGTK);
+
 	AtomicBoolean windowOpenFired = new AtomicBoolean(false);
 	AtomicBoolean childCompleted = new AtomicBoolean(false);
 	AtomicBoolean visibilityShowed = new AtomicBoolean(false);
@@ -1380,6 +1383,8 @@ public void completed(ProgressEvent event) {
  */
 @Test
 public void test_VisibilityWindowListener_eventSize() {
+	assumeFalse("Not currently working on Linux, see https://github.com/eclipse-platform/eclipse.platform.swt/issues/1564", SwtTestUtil.isGTK);
+
 	shell.setSize(200,300);
 	AtomicBoolean childCompleted = new AtomicBoolean(false);
 	AtomicReference<Point> result = new AtomicReference<>(new Point(0,0));