Compute Compiler.proxyConstant on demand.

pkg/compiler/lib/src/resolution/resolution.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 dart2js.resolution;
 
 import 'dart:collection' show Queue;
 
 import '../common/names.dart' show
     Identifiers;
@@ skipping 580 matching lines @@
       // TODO(johnniwinther): Check matching type variables and
       // empty extends/implements clauses.
     }
   }
 
   void _postProcessClassElement(BaseClassElementX element) {
     for (MetadataAnnotation metadata in element.implementation.metadata) {
       metadata.ensureResolved(compiler);
       ConstantValue value =
           compiler.constants.getConstantValue(metadata.constant);
-      if (!element.isProxy && value == compiler.proxyConstant) {
+      if (!element.isProxy && compiler.isProxyConstant(value)) {
         element.isProxy = true;
       }
     }
 
     // Force resolution of metadata on non-instance members since they may be
     // inspected by the backend while emitting. Metadata on instance members is
     // handled as a result of processing instantiated class members in the
     // enqueuer.
     // TODO(ahe): Avoid this eager resolution.
     element.forEachMember((_, Element member) {
@@ skipping 426 matching lines @@
   TreeElements get treeElements {
     assert(invariant(this, _treeElements !=null,
         message: "TreeElements have not been computed for $this."));
     return _treeElements;
   }
 
   void reuseElement() {
     _treeElements = null;
   }
 }