Bug 574040, fix test so that it doesn't have an underlying missing menu label layout issue on Windows 7 64bit

toolkit/content/tests/widgets/test_popupincontent.xul

@@ -16,7 +16,7 @@
 
 <hbox>
   <spacer width="100"/>
-  <menu id="menu">
+  <menu id="menu" label="Menu">
     <menupopup style="margin:10px;" id="popup" onpopupshown="popupShown()" onpopuphidden="nextTest()">
       <menuitem label="One"/>
       <menuitem label="Two"/>