Inline instance object hash code into object header on 64 bit.

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 603911f3ee7034b0895c0baae47e38db80673eda..98874442f2163792b48a13b45bfed0fef68a9123 100644
--- a/runtime/lib/object_patch.dart
+++ b/runtime/lib/object_patch.dart
@@ -21,10 +21,9 @@ class Object {
     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;