Handle named mixin application in emitter

pkg/compiler/lib/src/js_emitter/program_builder/collector.dart

 // Copyright (c) 2015, 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 dart2js.js_emitter.program_builder;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 211 matching lines @@
     void addClassesWithSuperclasses(Iterable<ClassEntity> classes) {
       for (ClassEntity cls in classes) {
         addClassWithSuperclasses(cls);
       }
     }
 
     // 1. We need to generate all classes that are instantiated.
     addClassesWithSuperclasses(instantiatedClasses);
 
     // 2. Add all classes used as mixins.
-    Set<ClassEntity> mixinClasses = new Set<ClassEntity>();
-    for (ClassEntity cls in neededClasses) {
-      _elementEnvironment.forEachMixin(cls, (ClassEntity mixinClass) {
-        mixinClasses.add(mixinClass);
-      });
-    }
+    Set<ClassEntity> mixinClasses = neededClasses
+        .where(_elementEnvironment.isMixinApplication)
+        .map(_elementEnvironment.getEffectiveMixinClass)
+        .toSet();
     neededClasses.addAll(mixinClasses);
 
     // 3. Find all classes needed for rti.
     // It is important that this is the penultimate step, at this point,
     // neededClasses must only contain classes that have been resolved and
     // codegen'd. The rtiNeededClasses may contain additional classes, but
     // these are thought to not have been instantiated, so we neeed to be able
     // to identify them later and make sure we only emit "empty shells" without
     // fields, etc.
     classesOnlyNeededForRti = new Set<ClassElement>();
@@ skipping 109 matching lines @@
   }
 
   void collect() {
     computeNeededDeclarations();
     computeNeededConstants();
     computeNeededStatics();
     computeNeededStaticNonFinalFields();
     computeNeededLibraries();
   }
 }