dart2js: get:hashCode methods to avoid Object.hashCode

pkg/compiler/lib/src/library_loader.dart

Index: pkg/compiler/lib/src/library_loader.dart
diff --git a/pkg/compiler/lib/src/library_loader.dart b/pkg/compiler/lib/src/library_loader.dart
index be0cb41499551e76dde6f66fecb715fbc4dac788..0797b8fc4db316fb4440aa775e03f6c98a3c5da4 100644
--- a/pkg/compiler/lib/src/library_loader.dart
+++ b/pkg/compiler/lib/src/library_loader.dart
@@ -916,10 +916,9 @@ class ExportLink {
 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