Handle @proxy classes in type checker.

tests/compiler/dart2js/resolver_test.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 "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import 'dart:collection';
 
 import "../../../sdk/lib/_internal/compiler/implementation/resolution/resolution.dart";
@@ skipping 821 matching lines @@
          class String {}
          class num {}
          class Function {}
          class List<E> {}
          class Map {}
          class Closure {}
          class Null {}
          class StackTrace {}
          class Dynamic_ {}
          class Type {}
-         class Object { Object() : super(); }''';
+         class Object { Object() : super(); }
+         const proxy = 0;''';
   resolveConstructor(script, "Object o = new Object();", "Object", "", 1,
                      expectedWarnings: [],
                      expectedErrors: [MessageKind.SUPER_INITIALIZER_IN_OBJECT],
                      corelib: CORELIB_WITH_INVALID_OBJECT);
 }
 
 map(ResolverVisitor visitor) {
   CollectingTreeElements elements = visitor.mapping;
   return elements.map;
 }
@@ skipping 133 matching lines @@
       }""";
   asyncTest(() => compileScript(script2).then((compiler) {
     expect(compiler,
         [MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS],
         [MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_CONSTRUCTOR,
          MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_CONSTRUCTOR,
          MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_FIELD,
          MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_FIELD]);
   }));
 }