dart2js: Don't reference mixins when they are only used for RTI.

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

 // Copyright (c) 2014, 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.
 
 library dart2js.js_emitter.program_builder;
 
 import 'js_emitter.dart' show computeMixinClass;
 import 'model.dart';
 
 import '../common.dart';
@@ skipping 70 matching lines @@
     outputs.setAll(1, deferredOutputs);
 
     Program result =
         new Program(outputs, _task.outputContainsConstantList, _buildLoadMap());
 
     // Resolve the superclass references after we've processed all the classes.
     _classes.forEach((ClassElement element, Class c) {
       if (element.superclass != null) {
         c.setSuperclass(_classes[element.superclass]);
       }
-      if (element.isMixinApplication) {
-        MixinApplication mixinApplication = c;
-        mixinApplication.setMixinClass(_classes[computeMixinClass(element)]);
+      if (c is MixinApplication) {
+        c.setMixinClass(_classes[computeMixinClass(element)]);
       }
     });
 
     _markEagerClasses();
 
     return result;
   }
 
   void _markEagerClasses() {
     _markEagerInterceptorClasses();
@@ skipping 188 matching lines @@
     });
 
     String name = namer.getNameOfClass(element);
     String holderName = namer.globalObjectFor(element);
     Holder holder = _registry.registerHolder(holderName);
     bool onlyForRti = _task.typeTestRegistry.rtiNeededClasses.contains(element);
     bool isInstantiated =
         _compiler.codegenWorld.directlyInstantiatedClasses.contains(element);
 
     Class result;
-    if (element.isMixinApplication) {
+    if (element.isMixinApplication && !onlyForRti) {
       result = new MixinApplication(element,
                                     name, holder, methods, fields,
                                     isDirectlyInstantiated: isInstantiated,
                                     onlyForRti: onlyForRti);
     } else {
       result = new Class(element,
                          name, holder, methods, fields,
                          isDirectlyInstantiated: isInstantiated,
                          onlyForRti: onlyForRti);
     }
@@ skipping 134 matching lines @@
       _registry.registerConstant(outputUnit, constantValue);
       assert(!_constants.containsKey(constantValue));
       String name = namer.constantName(constantValue);
       String constantObject = namer.globalObjectForConstant(constantValue);
       Holder holder = _registry.registerHolder(constantObject);
       Constant constant = new Constant(name, holder, constantValue);
       _constants[constantValue] = constant;
     }
   }
 }