Use Entity in native_data.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 31afbc6849b8c39014b2977634a562ebccf9d69b..3d1c6c6da40e7d010eacce59288a07eb92ba8d04 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -2002,6 +2002,15 @@ class _CompilerElementEnvironment implements ElementEnvironment {
   }
 
   @override
+  ClassEntity getSuperClass(ClassElement cls) {
+    cls = cls.superclass;
+    while (cls != null && cls.isUnnamedMixinApplication) {
+      cls = cls.superclass;
+    }
+    return cls;
+  }
+
+  @override
   void forEachMixin(ClassElement cls, void f(ClassElement mixin)) {
     for (; cls != null; cls = cls.superclass) {
       if (cls.isMixinApplication) {