Add NoSafepointScope to ObjectPointerVisitor.

runtime/vm/allocation.h

 // Copyright (c) 2013, 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.
 
 #ifndef VM_ALLOCATION_H_
 #define VM_ALLOCATION_H_
 
 #include "platform/assert.h"
 #include "vm/base_isolate.h"
 #include "vm/globals.h"
@@ skipping 116 matching lines @@
   // operator to be public.
 
   // Disallow explicit deallocation of nodes. Nodes can only be
   // deallocated by invoking DeleteAll() on the zone they live in.
   void operator delete(void* pointer) { UNREACHABLE(); }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ZoneAllocated);
 };
 
+
+
+// Within a NoSafepointScope, the thread must not reach any safepoint. Used
+// around code that manipulates raw object pointers directly without handles.
+#if defined(DEBUG)
+class NoSafepointScope : public StackResource {
+ public:
+  NoSafepointScope();
+  ~NoSafepointScope();
+ private:
+  DISALLOW_COPY_AND_ASSIGN(NoSafepointScope);
+};
+#else  // defined(DEBUG)
+class NoSafepointScope : public ValueObject {
+ public:
+  NoSafepointScope() {}
+ private:
+  DISALLOW_COPY_AND_ASSIGN(NoSafepointScope);
+};
+#endif  // defined(DEBUG)
+
 }  // namespace dart
 
 #endif  // VM_ALLOCATION_H_