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

runtime/lib/object.cc

Index: runtime/lib/object.cc
diff --git a/runtime/lib/object.cc b/runtime/lib/object.cc
index b7dcea3a2088351939f96dbb7ef5d1c8b07932bf..f0739adc3acdfdebdf0a6430ee4fdc9d0bbde187 100644
--- a/runtime/lib/object.cc
+++ b/runtime/lib/object.cc
@@ -42,17 +42,25 @@ DEFINE_NATIVE_ENTRY(Object_getHash, 1) {
   // Please note that no handle is created for the argument.
   // This is safe since the argument is only used in a tail call.
   // The performance benefit is more than 5% when using hashCode.
+#if defined(HASH_IN_OBJECT_HEADER)
+  return Smi::New(Object::GetCachedHash(arguments->NativeArgAt(0)));
+#else
   Heap* heap = isolate->heap();
   ASSERT(arguments->NativeArgAt(0)->IsDartInstance());
   return Smi::New(heap->GetHash(arguments->NativeArgAt(0)));
+#endif
 }
 
 
 DEFINE_NATIVE_ENTRY(Object_setHash, 2) {
-  const Instance& instance = Instance::CheckedHandle(arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(Smi, hash, arguments->NativeArgAt(1));
+#if defined(HASH_IN_OBJECT_HEADER)
+  Object::SetCachedHash(arguments->NativeArgAt(0), hash.Value());
+#else
+  const Instance& instance = Instance::CheckedHandle(arguments->NativeArgAt(0));
   Heap* heap = isolate->heap();
   heap->SetHash(instance.raw(), hash.Value());
+#endif
   return Object::null();
 }