Resubmit change 6302 after fixing the compiler warning on older GCC compiler versions:

vm/visitor.h

 // Copyright (c) 2011, 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_VISITOR_H_
 #define VM_VISITOR_H_
 
 #include "vm/globals.h"
 
 namespace dart {
@@ skipping 10 matching lines @@
   virtual void VisitPointers(RawObject** first, RawObject** last) = 0;
 
   // len argument is the number of pointers to visit starting from 'p'.
   void VisitPointers(RawObject** p, intptr_t len) {
     VisitPointers(p, (p + len - 1));
   }
 
   void VisitPointer(RawObject** p) { VisitPointers(p , p); }
 };
 
+
+// An object finder visitor interface.
+class FindObjectVisitor {
+ public:
+  virtual ~FindObjectVisitor() {}
+
+  // Check if object matches find condition.
+  virtual bool FindObject(RawObject* obj) = 0;
+};
+
 }  // namespace dart
 
 #endif  // VM_VISITOR_H_