Revert "Revert "Fix x.runtimeType for native classes""

sdk/lib/_internal/compiler/implementation/lib/js_rti.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_rti.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_rti.dart b/sdk/lib/_internal/compiler/implementation/lib/js_rti.dart
index b8f4e7d3b618e939118ada736e7a661a3f595984..fd64f48144278759c59dc44513f79f1dc68821af 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_rti.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_rti.dart
@@ -32,7 +32,7 @@ class TypeImpl implements Type {
 }
 
 String getClassName(var object) {
-  return JS('String', r'#.constructor.builtin$cls', object);
+  return JS('String', r'#.constructor.builtin$cls', getInterceptor(object));
 }
 
 String getRuntimeTypeAsString(List runtimeType) {
@@ -80,6 +80,11 @@ String getRuntimeTypeString(var object) {
   return "$className${joinArguments(typeInfo, 0)}";
 }
 
+Type getRuntimeType(var object) {
+  String type = getRuntimeTypeString(object);
+  return new TypeImpl(type);
+}
+
 bool isJsFunction(var o) => JS('bool', r'typeof # == "function"', o);
 
 Object invoke(function, arguments) {