Avoid crash for type variables in mixed in fields.

pkg/compiler/lib/src/closure.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.
 
 import 'common/names.dart' show Identifiers;
 import 'common/resolution.dart' show ParsingContext, Resolution;
 import 'common/tasks.dart' show CompilerTask, Measurer;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
 import 'constants/expressions.dart';
@@ skipping 1514 matching lines @@
   int get hashCode => typeVariable.hashCode;
 
   bool operator ==(other) {
     if (other is! TypeVariableLocal) return false;
     return typeVariable == other.typeVariable;
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write('type_variable_local(');
-    if (memberContext.enclosingClass != null) {
-      sb.write(memberContext.enclosingClass.name);
-      sb.write('.');
-    }
-    sb.write(memberContext.name);
-    sb.write('#');
-    sb.write(name);
+    sb.write(typeVariable);
     sb.write(')');
     return sb.toString();
   }
 }
 
 ///
 /// Move the below classes to a JS model eventually.
 ///
 abstract class JSEntity implements MemberEntity {
   Local get declaredEntity;
 }
 
 abstract class PrivatelyNamedJSEntity implements JSEntity {
   Entity get rootOfScope;
 }