Revert mixin fix r41424 until mirrors issue 21474 is fixed.

tests/lib/mirrors/mirrors_reader.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 LICESNE file.
 
 library mirrors.reader;
 
 import 'dart:mirrors';
 import 'mirrors_visitor.dart';
 
 class ReadError {
@@ skipping 195 matching lines @@
           () => mirror.isGenerativeConstructor);
     visit(mirror, 'isGetter', () => mirror.isGetter);
     visit(mirror, 'isOperator', () => mirror.isOperator);
     visit(mirror, 'isRedirectingConstructor',
           () => mirror.isRedirectingConstructor);
     visit(mirror, 'isRegularMethod', () => mirror.isRegularMethod);
     visit(mirror, 'isSetter', () => mirror.isSetter);
     visit(mirror, 'isStatic', () => mirror.isStatic);
     visit(mirror, 'isSynthetic', () => mirror.isSynthetic);
     visit(mirror, 'parameters', () => mirror.parameters);
-    // visit(mirror, 'returnType', () => mirror.returnType);  // Issue 21474.
+    visit(mirror, 'returnType', () => mirror.returnType);
     visit(mirror, 'source', () => mirror.source);
   }
 
   visitParameterMirror(ParameterMirror mirror) {
     super.visitParameterMirror(mirror);
     bool hasDefaultValue =
         visit(mirror, 'hasDefaultValue', () => mirror.hasDefaultValue);
     if (hasDefaultValue) {
       visit(mirror, 'defaultValue', () => mirror.defaultValue);
     }
     visit(mirror, 'isNamed', () => mirror.isNamed);
     visit(mirror, 'isOptional', () => mirror.isOptional);
-    // visit(mirror, 'type', () => mirror.type);  // Issue 21474.
+    visit(mirror, 'type', () => mirror.type);
   }
 
   visitSourceLocation(SourceLocation location) {
 
   }
 
   visitTypedefMirror(TypedefMirror mirror) {
     super.visitTypedefMirror(mirror);
     visit(mirror, 'referent', () => mirror.referent);
   }
@@ skipping 11 matching lines @@
     super.visitTypeVariableMirror(mirror);
     visit(mirror, 'upperBound', () => mirror.upperBound);
     visit(mirror, 'isStatic', () => mirror.isStatic);
   }
 
   visitVariableMirror(VariableMirror mirror) {
     super.visitVariableMirror(mirror);
     visit(mirror, 'isConst', () => mirror.isConst);
     visit(mirror, 'isFinal', () => mirror.isFinal);
     visit(mirror, 'isStatic', () => mirror.isStatic);
-    // visit(mirror, 'type', () => mirror.type);  // Issue 21474.
+    visit(mirror, 'type', () => mirror.type);
   }
 }