Implement a 2-pass heap verification algorithm.

runtime/vm/heap_profiler.h

 // 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.
 
 #ifndef VM_HEAP_PROFILER_H_
 #define VM_HEAP_PROFILER_H_
 
 #include <set>
 
 #include "include/dart_api.h"
@@ skipping 279 matching lines @@
 
  private:
   HeapProfilerRootVisitor* visitor_;
   DISALLOW_COPY_AND_ASSIGN(HeapProfilerWeakRootVisitor);
 };
 
 
 // Writes a sub-record to the heap dump for every object in the heap.
 class HeapProfilerObjectVisitor : public ObjectVisitor {
  public:
-  explicit HeapProfilerObjectVisitor(HeapProfiler* profiler)
-      : profiler_(profiler) {
+  HeapProfilerObjectVisitor(Isolate* isolate, HeapProfiler* profiler)
+      : ObjectVisitor(isolate), profiler_(profiler) {
   }
 
   virtual void VisitObject(RawObject* obj);
 
  private:
   HeapProfiler* profiler_;
   DISALLOW_COPY_AND_ASSIGN(HeapProfilerObjectVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_HEAP_PROFILER_H_