Sped up hashCode by removing megamorphic call to _identityHashCode.

runtime/lib/object_patch.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.
 
 patch class Object {
 
   // The VM has its own implementation of equals.
   bool operator ==(other) native "Object_equals";
 
   // Helpers used to implement hashCode. If a hashCode is used, we remember it
   // in a weak table in the VM. A new hashCode value is calculated using a
   // number generator.
   static final _hashCodeRnd = new Random();
 
   static _getHash(obj) native "Object_getHash";
   static _setHash(obj, hash) native "Object_setHash";
 
-  /* patch */ int get hashCode => _identityHashCode;
-
-  int get _identityHashCode {
-    var result = _getHash(this);
+  // Shared static implentation for hashCode and _identityHashCode.
+  static int _objectHashCode(obj) {
+    var result = _getHash(obj);
     if (result == 0) {
       // We want the hash to be a Smi value greater than 0.
       result = _hashCodeRnd.nextInt(0x40000000);
       while (result == 0) {
         result = _hashCodeRnd.nextInt(0x40000000);
       }
-      _setHash(this, result);
+      _setHash(obj, result);
     }
     return result;
   }
 
+  /* patch */ int get hashCode => _objectHashCode(this);
+  int get _identityHashCode => _objectHashCode(this);
+
   /* patch */ String toString() native "Object_toString";
   // A statically dispatched version of Object.toString.
   static String _toString(obj) native "Object_toString";
 
   _noSuchMethod(bool isMethod,
                 String memberName,
                 int type,
                 List arguments,
                 Map<String, dynamic> namedArguments)
       native "Object_noSuchMethod";
@@ skipping 24 matching lines @@
   _as(instantiator_type_arguments, type) native "Object_as";
 
   static _symbolMapToStringMap(Map<Symbol, dynamic> map) {
     var result = new Map<String, dynamic>();
     map.forEach((Symbol key, value) {
       result[internal.Symbol.getName(key)] = value;
     });
     return result;
   }
 }