Fix NOTREACHED triggered by MenuItemView::GetAcceleratorText

A recent change to accessibility on Chrome OS is triggering a call to
MenuItemView::GetAccessibleState on a MenuItemView that has a delegate
but no command id, which asserts in MenuModelAdapter when we try to
look up a command that's not there.

The fix is to not call MenuModelAdapter::GetAccelerator to look up a
command when the command is zero.

BUG=230107,232079

Review URL: https://codereview.chromium.org/14161006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194665 0039d316-1c4b-4281-b951-d872f2087c98

ui/views/controls/menu/menu_item_view.cc

@@ -1009,7 +1009,7 @@ string16 MenuItemView::GetAcceleratorText() {
     return string16();
 
   ui::Accelerator accelerator;
-  return (GetDelegate() &&
+  return (GetDelegate() && GetCommand() &&
           GetDelegate()->GetAccelerator(GetCommand(), &accelerator)) ?
       accelerator.GetShortcutText() : string16();
 }