Fix initially selected CheckBox rendering in Safari in v7 compatibility package (#11024) (#11456)

This fix was already applied to com.vaadin.client.ui.VCheckBox but the committer forget to apply the same fix to the com.vaadin.v7.client.ui.VCheckBox. Some people are still temporarely using the checkbox from the compatibility package.

compatibility-client/src/main/java/com/vaadin/v7/client/ui/VCheckBox.java

@@ -16,7 +16,9 @@
 
 package com.vaadin.v7.client.ui;
 
+import com.google.gwt.core.client.Scheduler;
 import com.google.gwt.dom.client.Element;
+import com.google.gwt.dom.client.Style;
 import com.google.gwt.event.dom.client.ClickEvent;
 import com.google.gwt.event.dom.client.ClickHandler;
 import com.google.gwt.user.client.DOM;
@@ -106,4 +108,21 @@ public class VCheckBox extends com.google.gwt.user.client.ui.CheckBox
     public void setAriaInvalid(boolean invalid) {
         AriaHelper.handleInputInvalid(getCheckBoxElement(), invalid);
     }
+
+    @Override
+    protected void onAttach() {
+        super.onAttach();
+
+        if (BrowserInfo.get().isSafari()) {
+            /*
+             * Sometimes Safari does not render checkbox correctly when
+             * attaching. Setting the visibility to hidden and a bit later
+             * restoring will make everything just fine.
+             */
+            getElement().getStyle().setVisibility(Style.Visibility.HIDDEN);
+            Scheduler.get().scheduleFinally(() -> {
+                getElement().getStyle().setVisibility(Style.Visibility.VISIBLE);
+            });
+        }
+    }
 }