Avoid reading RawObject::class_ directly in the runtime.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 31c0fbc4a3ca519100ab126baa8ed6fe59535243..d6b2516cee60f8f4e6a06af88ec7eaa59c1f41a9 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -4886,12 +4886,7 @@ RawClass* Object::clazz() const {
   if ((raw_value & kSmiTagMask) == kSmiTag) {
     return Smi::Class();
   }
-  RawClass* result = raw_->ptr()->class_;
-  ASSERT(result->ptr()->index_ ==
-      RawObject::ClassTag::decode(raw_->ptr()->tags_));
-  ASSERT(Isolate::Current()->class_table()->At(
-      RawObject::ClassTag::decode(raw_->ptr()->tags_)) == result);
-  return result;
+  return Isolate::Current()->class_table()->At(raw()->GetClassIndex());
 }
 
 
@@ -4910,8 +4905,13 @@ void Object::SetRaw(RawObject* value) {
   ASSERT(isolate_heap->Contains(reinterpret_cast<uword>(raw_->ptr())) ||
          vm_isolate_heap->Contains(reinterpret_cast<uword>(raw_->ptr())));
 #endif
-  set_vtable((raw_ == null_) ?
-             handle_vtable_ : raw_->ptr()->class_->ptr()->handle_vtable_);
+  if (raw_ == null_) {
+    set_vtable(handle_vtable_);
+  } else {
+    RawClass* raw_class =
+      Isolate::Current()->class_table()->At(raw_->GetClassIndex());
+    set_vtable(raw_class->ptr()->handle_vtable_);
+  }
 }