Find native classes with mixins in NativeClassFinder

pkg/compiler/lib/src/resolution/resolution_strategy.dart

Index: pkg/compiler/lib/src/resolution/resolution_strategy.dart
diff --git a/pkg/compiler/lib/src/resolution/resolution_strategy.dart b/pkg/compiler/lib/src/resolution/resolution_strategy.dart
index a2c5e94cb449fee626951b20f00ece9cabda751f..a6b9268febbb426f5d48c8bd051baedaf092e4e8 100644
--- a/pkg/compiler/lib/src/resolution/resolution_strategy.dart
+++ b/pkg/compiler/lib/src/resolution/resolution_strategy.dart
@@ -306,9 +306,16 @@ class _CompilerElementEnvironment implements ElementEnvironment {
   }
 
   @override
-  ClassEntity getSuperClass(ClassElement cls) {
+  ClassEntity getSuperClass(ClassElement cls,
+      {bool skipUnnamedMixinApplications: false}) {
     cls.ensureResolved(_resolution);
-    return cls.superclass;
+    ClassElement superclass = cls.superclass;
+    if (skipUnnamedMixinApplications) {
+      while (superclass != null && superclass.isUnnamedMixinApplication) {
+        superclass = superclass.superclass;
+      }
+    }
+    return superclass;
   }
 
   @override