Add NoSafepointScope to ObjectPointerVisitor.

runtime/vm/allocation.cc

 // 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.
 
 #include "vm/allocation.h"
 
 #include "platform/assert.h"
 #include "vm/isolate.h"
 #include "vm/zone.h"
 
@@ skipping 20 matching lines @@
 
 
 void StackResource::UnwindAbove(Thread* thread, StackResource* new_top) {
   StackResource* current_resource = thread->top_resource();
   while (current_resource != new_top) {
     current_resource->~StackResource();
     current_resource = thread->top_resource();
   }
 }
 
+
+#if defined(DEBUG)
+NoSafepointScope::NoSafepointScope() : StackResource(Thread::Current()) {
+  thread()->IncrementNoSafepointScopeDepth();
+}
+
+
+NoSafepointScope::~NoSafepointScope() {
+  thread()->DecrementNoSafepointScopeDepth();
+}
+#endif  // defined(DEBUG)
+
 }  // namespace dart