Small steps towards deferred loading.

pkg/front_end/lib/src/fasta/source/source_library_builder.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.source_library_builder;
 
 import 'package:kernel/ast.dart' show AsyncMarker, ProcedureKind;
 
 import '../combinator.dart' show Combinator;
 
@@ skipping 112 matching lines @@
 
   void addImport(
       List<MetadataBuilder> metadata,
       String uri,
       Unhandled conditionalUris,
       String prefix,
       List<Combinator> combinators,
       bool deferred,
       int charOffset,
       int prefixCharOffset) {
-    imports.add(new Import(this, loader.read(resolve(uri)), prefix, combinators,
-        charOffset, prefixCharOffset));
+    imports.add(new Import(this, loader.read(resolve(uri)), deferred, prefix,
+        combinators, charOffset, prefixCharOffset));
   }
 
   void addPart(List<MetadataBuilder> metadata, String path) {
     Uri resolvedUri;
     Uri newFileUri;
     if (uri.scheme == "dart") {
       resolvedUri = new Uri(scheme: "dart", path: "${uri.path}/$path");
       newFileUri = fileUri.resolve(path);
     } else {
       resolvedUri = uri.resolve(path);
@@ skipping 411 matching lines @@
   /// synthesize type variables on the factory matching the class'.
   void addFactoryDeclaration(
       ProcedureBuilder procedure, DeclarationBuilder<T> factoryDeclaration) {
     factoryDeclarations[procedure] = factoryDeclaration;
   }
 
   Scope toScope(Scope parent) {
     return new Scope(members, setters, parent, isModifiable: false);
   }
 }