Small steps towards deferred loading.

pkg/front_end/lib/src/fasta/import.dart

 // Copyright (c) 2016, 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 fasta.import;
 
 import 'builder/builder.dart' show Builder, LibraryBuilder, PrefixBuilder;
 
 import 'combinator.dart' show Combinator;
 
 typedef void AddToScope(String name, Builder member);
 
 class Import {
   /// The library that is importing [imported];
   final LibraryBuilder importer;
 
   /// The library being imported.
   final LibraryBuilder imported;
 
+  final bool deferred;
+
   final String prefix;
 
   final List<Combinator> combinators;
 
   final int charOffset;
 
   final int prefixCharOffset;
 
-  Import(this.importer, this.imported, this.prefix, this.combinators,
-      this.charOffset, this.prefixCharOffset);
+  Import(this.importer, this.imported, this.deferred, this.prefix,
+      this.combinators, this.charOffset, this.prefixCharOffset);
 
   Uri get fileUri => importer.fileUri;
 
   void finalizeImports(LibraryBuilder importer) {
     AddToScope add;
     PrefixBuilder prefix;
     if (this.prefix == null) {
       add = (String name, Builder member) {
         importer.addToScope(name, member, charOffset, true);
       };
     } else {
-      prefix = new PrefixBuilder(this.prefix, importer, prefixCharOffset);
+      prefix =
+          new PrefixBuilder(this.prefix, deferred, importer, prefixCharOffset);
       add = (String name, Builder member) {
         if (member.isSetter) {
           prefix.exports.setters[name] = member;
         } else {
           prefix.exports.local[name] = member;
         }
       };
     }
     imported.exports.forEach((String name, Builder member) {
       if (combinators != null) {
         for (Combinator combinator in combinators) {
           if (combinator.isShow && !combinator.names.contains(name)) return;
           if (combinator.isHide && combinator.names.contains(name)) return;
         }
       }
       add(name, member);
     });
     if (prefix != null) {
       Builder existing = importer.addBuilder(prefix.name, prefix, charOffset);
       if (existing == prefix) {
         importer.addToScope(prefix.name, prefix, prefixCharOffset, true);
       }
     }
   }
 }