Fix x.runtimeType for native classes

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

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index 536de66b97f5b2d2b4691cb97abf1807d6e9f9ed..009567233014405d307214ad8abf97372dbc2f15 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -177,6 +177,8 @@ abstract class Backend {
   ClassElement get boolImplementation => compiler.boolClass;
   ClassElement get nullImplementation => compiler.nullClass;
 
+  ClassElement defaultSuperclass(ClassElement element) => compiler.objectClass;
+
   bool isDefaultNoSuchMethodImplementation(Element element) {
     assert(element.name == Compiler.NO_SUCH_METHOD);
     ClassElement classElement = element.getEnclosingClass();