Fixed few more issues with upgrader and custom event identitiy

tools/dom/src/dartium_CustomElementSupport.dart

Index: tools/dom/src/dartium_CustomElementSupport.dart
diff --git a/tools/dom/src/dartium_CustomElementSupport.dart b/tools/dom/src/dartium_CustomElementSupport.dart
index d80f2c45f571d693e83fe5758a34cfcc54bd2a23..f221be5a4fceb990b3185194a1bdb468f2f649a6 100644
--- a/tools/dom/src/dartium_CustomElementSupport.dart
+++ b/tools/dom/src/dartium_CustomElementSupport.dart
@@ -31,6 +31,10 @@ class _VMElementUpgrader implements ElementUpgrader {
       throw new UnsupportedError('Element is incorrect type');
     }
 
+    // Remember Dart class to tagName for any upgrading done in wrap_jso.
+    var tag = element['localName'];
+    _knownCustomeElements[tag] = _type;
+
     return createCustomUpgrader(_nativeType, element);
   }
 }