Removing explicit custom element upgrade for Dartium

tools/dom/src/dartium_Platform.dart

Index: tools/dom/src/dartium_Platform.dart
diff --git a/tools/dom/src/dartium_Platform.dart b/tools/dom/src/dartium_Platform.dart
index 34fdecced846032215b4712995dbfd2a21350526..5ae23c94adb458ef3a67288e4980f4b366ea91f7 100644
--- a/tools/dom/src/dartium_Platform.dart
+++ b/tools/dom/src/dartium_Platform.dart
@@ -24,15 +24,8 @@ class Platform {
    *
    * This is needed to cover timing scenarios which the custom element polyfill
    * does not cover.
-   *
-   * This is also a workaround for dartbug.com/12642 in Dartium.
    */
   static void upgradeCustomElements(Node node) {
     // no-op, provided for dart2js polyfill.
-    if (node is Element) {
-      (node as Element).queryAll('*');
-    } else {
-      node.nodes.forEach(upgradeCustomElements);
-    }
   }
 }