Implement a 2-pass heap verification algorithm.

runtime/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 23 matching lines @@
  private:
   Isolate* isolate_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ObjectPointerVisitor);
 };
 
 
 // An object visitor interface.
 class ObjectVisitor {
  public:
+  explicit ObjectVisitor(Isolate* isolate) : isolate_(isolate) {}
+
   virtual ~ObjectVisitor() {}
 
+  Isolate* isolate() const { return isolate_; }
+
   // Invoked for each object.
   virtual void VisitObject(RawObject* obj) = 0;
+
+ private:
+  Isolate* isolate_;
+
+  DISALLOW_COPY_AND_ASSIGN(ObjectVisitor);
 };
 
 
 // An object finder visitor interface.
 class FindObjectVisitor {
  public:
   explicit FindObjectVisitor(Isolate* isolate) : isolate_(isolate) {}
   virtual ~FindObjectVisitor() {}
 
   // Check if object matches find condition.
   virtual bool FindObject(RawObject* obj) = 0;
 
  private:
   Isolate* isolate_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(FindObjectVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_VISITOR_H_