dart2js: get:hashCode methods to avoid Object.hashCode

pkg/compiler/lib/src/library_loader.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.library_loader;
 
 import 'dart:async';
 
 import 'common/names.dart' show Uris;
 import 'common/tasks.dart' show CompilerTask, Measurer;
@@ skipping 898 matching lines @@
 /**
  * A node in the library dependency graph.
  *
  * This class is used to collect the library dependencies expressed through
  * import and export tags, and as the work-list entry in computations of library
  * exports performed in [LibraryDependencyHandler.computeExports].
  */
 class LibraryDependencyNode {
   final LibraryElementX library;
 
-  // TODO(ahe): Remove [hashCodeCounter] and [hashCode] when
-  // VM implementation of Object.hashCode is not slow.
-  final int hashCode = ++hashCodeCounter;
-  static int hashCodeCounter = 0;
+  // Stored identity based hashCode for performance.
+  final int hashCode = _nextHash = (_nextHash + 100019).toUnsigned(30);
+  static int _nextHash = 0;
 
   /**
    * A linked list of the import tags that import [library] mapped to the
    * corresponding libraries. This is used to propagate exports into imports
    * after the export scopes have been computed.
    */
   Link<ImportLink> imports = const Link<ImportLink>();
 
   /// A linked list of all libraries directly exported by [library].
   Link<LibraryElement> exports = const Link<LibraryElement>();
@@ skipping 585 matching lines @@
   Future onLibrariesLoaded(LoadedLibraries results);
 
   /// Called whenever a library element is created.
   void onLibraryCreated(LibraryElement library);
 
   /// Called whenever a library is scanned from a script file.
   Future onLibraryScanned(LibraryElement library, LibraryLoader loader);
 }
 
 const _reuseLibrarySubtaskName = "Reuse library";