Handle @proxy classes in type checker.

tests/compiler/dart2js/cpa_inference_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 'dart:async';
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import '../../../sdk/lib/_internal/compiler/implementation/source_file.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/types/types.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/types/concrete_types_inferrer.dart';
@@ skipping 156 matching lines @@
   }
   class Function {}
   abstract class List<E> {
     factory List([int length]) {}
   }
   abstract class Map<K, V> {}
   class Closure {}
   class Type {}
   class StackTrace {}
   class Dynamic_ {}
-  bool identical(Object a, Object b) {}''';
+  bool identical(Object a, Object b) {}
+  const proxy = 0;''';
 
 Future<AnalysisResult> analyze(String code, {int maxConcreteTypeSize: 1000}) {
   Uri uri = new Uri(scheme: 'source');
   MockCompiler compiler = new MockCompiler(
       coreSource: CORELIB,
       enableConcreteTypeInference: true,
       maxConcreteTypeSize: maxConcreteTypeSize);
   compiler.sourceFiles[uri.toString()] =
       new StringSourceFile(uri.toString(), code);
   compiler.typesTask.concreteTypesInferrer.testMode = true;
@@ skipping 1513 matching lines @@
     testIsCheck,
     testSeenClasses,
     testIntDoubleNum,
     testConcreteTypeToTypeMask,
     testSelectors,
     testMixins,
     testClosures,
     testNestedFunctions,
   ], (f) => f()));
 }