VM: Reland Inline instance object hash code into object header on 64bit.

runtime/lib/object_patch.dart

Index: runtime/lib/object_patch.dart
diff --git a/runtime/lib/object_patch.dart b/runtime/lib/object_patch.dart
index 35ccc5884901d9a82d2475a3e20fc9644993ae27..a74d92a08f0723496fe5d520808946b63b8b6f4e 100644
--- a/runtime/lib/object_patch.dart
+++ b/runtime/lib/object_patch.dart
@@ -2,6 +2,9 @@
 // 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.
 
+int _getHash(obj) native "Object_getHash";
+int _setHash(obj, hash) native "Object_setHash";
+
 @patch
 class Object {
   // The VM has its own implementation of equals.
@@ -9,22 +12,18 @@ class Object {
   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.
+  // in a weak table in the VM (32 bit) or in the header of the object (64
+  // bit). A new hashCode value is calculated using a random number generator.
   static final _hashCodeRnd = new Random();
 
-  // Shared static implementation for hashCode and _identityHashCode.
-  static _getHash(obj) native "Object_getHash";
-  static _setHash(obj, hash) native "Object_setHash";
-
   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) {
+      do {
         result = _hashCodeRnd.nextInt(0x40000000);
-      }
+      } while (result == 0);
       _setHash(obj, result);
     }
     return result;