Handle @proxy classes in type checker.

sdk/lib/_internal/compiler/implementation/elements/elements.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.
 
 library elements;
 
 
 import '../tree/tree.dart';
 import '../util/util.dart';
 import '../resolution/resolution.dart';
@@ skipping 869 matching lines @@
   void set origin(ClassElement value);
   void set supertypeLoadState(int value);
   void set resolutionState(int value);
   void set nativeTagInfo(String value);
 
   bool isObject(Compiler compiler);
   bool isSubclassOf(ClassElement cls);
   bool implementsInterface(ClassElement intrface);
   bool hasFieldShadowedBy(Element fieldMember);
 
+  /// Returns `true` if this class has a @proxy annotation.
+  bool get isProxy;
+
   ClassElement ensureResolved(Compiler compiler);
 
   void addMember(Element element, DiagnosticListener listener);
   void addToScope(Element element, DiagnosticListener listener);
 
   void setDefaultConstructor(FunctionElement constructor, Compiler compiler);
 
   void addBackendMember(Element element);
   void reverseBackendMembers();
 
@@ skipping 83 matching lines @@
   Token get endToken;
 
   // TODO(kasperl): Try to get rid of these.
   void set annotatedElement(Element value);
   void set resolutionState(int value);
 
   MetadataAnnotation ensureResolved(Compiler compiler);
 }
 
 abstract class VoidElement extends Element {}