Prevent spurious "Could not determine ApplicationConnection" error when using the debug window

Change-Id: I3b5a8ac4f33c7e8828e34c46056b8ecd6c05a436

client/src/com/vaadin/client/debug/internal/VDebugWindow.java

@@ -45,6 +45,7 @@ import com.google.gwt.user.client.Window;
 import com.google.gwt.user.client.Window.Location;
 import com.google.gwt.user.client.ui.Button;
 import com.google.gwt.user.client.ui.FlowPanel;
+import com.google.gwt.user.client.ui.RootPanel;
 import com.google.gwt.user.client.ui.SimplePanel;
 import com.google.gwt.user.client.ui.Widget;
 import com.vaadin.client.ApplicationConnection;
@@ -714,6 +715,18 @@ public final class VDebugWindow extends VOverlay {
         }
     }
 
+    /**
+     * Gets the container element for this window. The debug window is always
+     * global to the document and not related to any
+     * {@link ApplicationConnection} in particular.
+     * 
+     * @return The global overlay container element.
+     */
+    @Override
+    public com.google.gwt.user.client.Element getOverlayContainer() {
+        return RootPanel.get().getElement();
+    }
+
     /*
      * Inner classes
      */