Addresses a ClassCastException seen in the editor from MemberBuilder

compiler/javatests/com/google/dart/compiler/resolver/NegativeResolverTest.java

 // Copyright (c) 2011, 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.
 
 package com.google.dart.compiler.resolver;
 
 import com.google.dart.compiler.CompilerTestCase;
 import com.google.dart.compiler.DartCompilationError;
 import com.google.dart.compiler.ast.DartUnit;
 import com.google.dart.compiler.testing.TestCompilerContext;
@@ skipping 71 matching lines @@
   public void testArrayLiteralNegativeTest() {
     checkSourceErrors(
         makeCode(
             "class A {",
             "  main() {",
             "    List<int, int> ints = [1];",
             "  }",
             "}"),
         errEx(TypeErrorCode.WRONG_NUMBER_OF_TYPE_ARGUMENTS, 3, 5, 14));
   }
-  
+
   public void testMapLiteralNegativeTest() {
     checkSourceErrors(
         makeCode(
             "class A {",
             "  main() {",
             "    Map<String, int, int> map = {'foo':1};",
             "  }",
             "}"),
             errEx(TypeErrorCode.WRONG_NUMBER_OF_TYPE_ARGUMENTS, 3, 5, 21));
   }
-  
+
   public void testCall1() {
     checkNumErrors("StaticInstanceCallNegativeTest.dart", 1);
   }
 
   public void testClassExtendsInterfaceNegativeTest() {
     checkNumErrors("ClassExtendsInterfaceNegativeTest.dart", 1);
   }
 
   public void tesClassImplementsUnknownInterfaceNegativeTest() {
     checkNumErrors("ClassImplementsUnknownInterfaceNegativeTest.dart", 1);
@@ skipping 109 matching lines @@
 
   private TestCompilerContext getContext() {
     return new TestCompilerContext() {
       @Override
       public void onError(DartCompilationError event) {
         errors.add(event);
       }
     };
   }
 }