Fix casts and type assertions on mixins used in native classes

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked;
 
   JavaScriptItemCompilationContext()
@@ skipping 597 matching lines @@
       ClassElement cls, Enqueuer enqueuer) {
     if (enqueuer.isResolutionQueue) {
       cls.ensureResolved(compiler);
       cls.forEachMember((ClassElement classElement, Element member) {
         if (member.isSynthesized) return;
         // All methods on [Object] are shadowed by [Interceptor].
         if (classElement == compiler.objectClass) return;
         Set<Element> set = interceptedElements.putIfAbsent(
             member.name, () => new Set<Element>());
         set.add(member);
-        if (classElement == jsInterceptorClass) return;
-        if (classElement.isMixinApplication) {
-          MixinApplicationElement mixinApplication = classElement;
-          assert(member.getEnclosingClass() == mixinApplication.mixin);
+      },
+      includeSuperAndInjectedMembers: true);
+
+      //  Walk superclass chain to find mixins.
+      for (; cls != null; cls = cls.superclass) {
+        if (cls.isMixinApplication) {
+          MixinApplicationElement mixinApplication = cls;
           classesMixedIntoNativeClasses.add(mixinApplication.mixin);
         }
-      },
-      includeSuperAndInjectedMembers: true);
+      }
     }
   }
 
   void addInterceptors(ClassElement cls,
                        Enqueuer enqueuer,
                        TreeElements elements) {
     if (enqueuer.isResolutionQueue) {
       cls.ensureResolved(compiler);
       cls.forEachMember((ClassElement classElement, Element member) {
           // All methods on [Object] are shadowed by [Interceptor].
@@ skipping 112 matching lines @@
   }
 
   JavaScriptItemCompilationContext createItemCompilationContext() {
     return new JavaScriptItemCompilationContext();
   }
 
   void enqueueHelpers(ResolutionEnqueuer world, TreeElements elements) {
     jsIndexingBehaviorInterface =
         compiler.findHelper(const SourceString('JavaScriptIndexingBehavior'));
     if (jsIndexingBehaviorInterface != null) {
+      jsIndexingBehaviorInterface.ensureResolved(compiler);
       world.registerIsCheck(jsIndexingBehaviorInterface.computeType(compiler),
                             elements);
       enqueue(
           world,
           compiler.findHelper(const SourceString('isJsIndexable')),
           elements);
       enqueue(
           world,
           compiler.findInterceptor(const SourceString('dispatchPropertyName')),
           elements);
@@ skipping 853 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }