Serialize data for LibraryElement.getImportsFor

pkg/compiler/lib/src/deferred_load.dart

 // Copyright (c) 2014, 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 deferred_load;
 
 import 'common/backend_api.dart' show Backend;
 import 'common/tasks.dart' show CompilerTask;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
@@ skipping 960 matching lines @@
 }
 
 /// A node in the deferred import graph.
 ///
 /// This class serves as the root node; the 'import' of the main library.
 class _DeferredImport {
   const _DeferredImport();
 
   /// Computes a suggestive name for this import.
   String computeImportDeferName(Compiler compiler) => 'main';
+
+  ImportElement get declaration => null;
+
+  String toString() => 'main';
 }
 
 /// A node in the deferred import graph defined by a deferred import directive.
 class _DeclaredDeferredImport implements _DeferredImport {
   final ImportElement declaration;
 
   _DeclaredDeferredImport(this.declaration);
 
   @override
   String computeImportDeferName(Compiler compiler) {
@@ skipping 26 matching lines @@
     assert(result != null);
     return result;
   }
 
   bool operator ==(other) {
     if (other is! _DeclaredDeferredImport) return false;
     return declaration == other.declaration;
   }
 
   int get hashCode => declaration.hashCode * 17;
+
+  String toString() => '$declaration';
 }