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

pkg/compiler/lib/src/js_emitter/old_emitter/emitter.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.
 
 part of dart2js.js_emitter;
 
 
 class OldEmitter implements Emitter {
   final Compiler compiler;
   final CodeEmitterTask task;
@@ skipping 412 matching lines @@
   }
 
   /** Needs defineClass to be defined. */
   jsAst.Expression buildInheritFrom() {
     jsAst.Expression result = js(r'''
         function() {
           function tmp() {}
           var hasOwnProperty = Object.prototype.hasOwnProperty;
           return function (constructor, superConstructor) {
             if (superConstructor == null) {
-              // TODO(21896): this test shouldn't be necessary. Without it
-              // we have a crash in language/mixin_only_for_rti and
-              // pkg/analysis_server/tool/spec/check_all_test.
-              if (constructor == null) return;
-
               // Fix up the the Dart Object class' prototype.
               var prototype = constructor.prototype;
               prototype.constructor = constructor;
               return prototype;
             }
             tmp.prototype = superConstructor.prototype;
             var object = new tmp();
             var properties = constructor.prototype;
             for (var member in properties) {
               if (hasOwnProperty.call(properties, member)) {
@@ skipping 34 matching lines @@
 
         var superclass = processedClasses.pending[cls];
 
         if (#needsMixinSupport) {
           if (superclass && superclass.indexOf("+") > 0) {
             var s = superclass.split("+");
             superclass = s[0];
             var mixinClass = s[1];
             finishClass(mixinClass);
             var mixin = allClasses[mixinClass];
-            // TODO(21896): this test shouldn't be necessary. Without it
-            // we have a crash in language/mixin_only_for_rti and
-            // pkg/analysis_server/tool/spec/check_all_test.
-            if (mixin) {
-              var mixinPrototype = mixin.prototype;
-              var clsPrototype = allClasses[cls].prototype;
-              for (var d in mixinPrototype) {
-                if (hasOwnProperty.call(mixinPrototype, d) &&
-                    !hasOwnProperty.call(clsPrototype, d))
-                  clsPrototype[d] = mixinPrototype[d];
-              }
+            var mixinPrototype = mixin.prototype;
+            var clsPrototype = allClasses[cls].prototype;
+            for (var d in mixinPrototype) {
+              if (hasOwnProperty.call(mixinPrototype, d) &&
+                  !hasOwnProperty.call(clsPrototype, d))
+                clsPrototype[d] = mixinPrototype[d];
             }
           }
         }
 
         // The superclass is only false (empty string) for the Dart Object
         // class.  The minifier together with noSuchMethod can put methods on
         // the Object.prototype object, and they show through here, so we check
         // that we have a string.
         if (!superclass || typeof superclass != "string") {
           inheritFrom(allClasses[cls], null);
@@ skipping 1576 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }