Fix infinite loop around FocusManager.onDocumentFocus_() when getFocusParent()...

Fix infinite loop around FocusManager.onDocumentFocus_() when getFocusParent() returns document.body (encountered the problem trying to add FocusManager to Print Preview).

BUG=276784

Review URL: https://codereview.chromium.org/398243003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284186 0039d316-1c4b-4281-b951-d872f2087c98

ui/webui/resources/js/cr/ui/focus_manager.js

@@ -29,20 +29,7 @@ cr.define('cr.ui', function() {
      * @private
      */
     isDescendantOf_: function(parent, child) {
-      var current = child;
-
-      while (current) {
-        current = current.parentNode;
-        if (typeof(current) == 'undefined' ||
-            typeof(current) == 'null' ||
-            current === document.body) {
-          return false;
-        } else if (current === parent) {
-          return true;
-        }
-      }
-
-      return false;
+      return parent && !(parent === child) && parent.contains(child);
     },
 
     /**