Compute Compiler.proxyConstant on demand.

pkg/compiler/lib/src/compiler.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.compiler_base;
 
 import 'dart:async' show
     EventSink,
     Future;
 
@@ skipping 830 matching lines @@
           reportWarning(NO_LOCATION_SPANNABLE,
              MessageKind.IMPORT_EXPERIMENTAL_MIRRORS,
               {'importChain': importChains.join(
                    MessageTemplate.IMPORT_EXPERIMENTAL_MIRRORS_PADDING)});
         }
       }
 
       functionClass.ensureResolved(this);
       functionApplyMethod = functionClass.lookupLocalMember('apply');
 
-      proxyConstant =
-          constants.getConstantValue(
-              resolver.constantCompiler.compileConstant(
-                  coreLibrary.find('proxy')));
-
       if (preserveComments) {
         return libraryLoader.loadLibrary(Uris.dart_mirrors)
             .then((LibraryElement libraryElement) {
           documentClass = libraryElement.find('Comment');
         });
       }
     }).then((_) => backend.onLibrariesLoaded(loadedLibraries));
   }
 
+  bool isProxyConstant(ConstantValue value) {
+    FieldElement field = coreLibrary.find('proxy');
+    if (field == null) return false;
+    if (!enqueuer.resolution.hasBeenResolved(field)) return false;
+    if (proxyConstant == null) {
+      proxyConstant =
+          constants.getConstantValue(
+              resolver.constantCompiler.compileConstant(field));
+    }
+    return proxyConstant == value;
+  }
+
   Element findRequiredElement(LibraryElement library, String name) {
     var element = library.find(name);
     if (element == null) {
       internalError(library,
           "The library '${library.canonicalUri}' does not contain required "
           "element: '$name'.");
       }
     return element;
   }
 
@@ skipping 910 matching lines @@
 
   @override
   InterfaceType streamType([DartType elementType]) {
     InterfaceType type = streamClass.computeType(compiler);
     if (elementType == null) {
       return streamClass.rawType;
     }
     return type.createInstantiation([elementType]);
   }
 }