Make ObjectGraph a StackResource.

runtime/vm/object_graph.h

 // Copyright (c) 2014, 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_OBJECT_GRAPH_H_
 #define VM_OBJECT_GRAPH_H_
 
+#include "vm/allocation.h"
 #include "vm/object.h"
 
 namespace dart {
 
 class Isolate;
 
 // Utility to traverse the object graph in an ordered fashion.
 // Example uses:
 // - find a retaining path from the isolate roots to a particular object, or
 // - determine how much memory is retained by some particular object(s).
-class ObjectGraph {
+class ObjectGraph : public StackResource {
  public:
   class Stack;
 
   // Allows climbing the search tree all the way to the root.
   class StackIterator {
    public:
     // The object this iterator currently points to.
     RawObject* Get() const;
     // Returns false if there is no parent.
     bool MoveToParent();
    private:
     StackIterator(const Stack* stack, intptr_t index)
         : stack_(stack), index_(index) { }
     const Stack* stack_;
     intptr_t index_;
     friend class ObjectGraph::Stack;
     DISALLOW_IMPLICIT_CONSTRUCTORS(StackIterator);
   };
 
   class Visitor {
    public:
     // Directs how the search should continue after visiting an object.
     enum Direction {
       kProceed,    // Recurse on this object's pointers.
       kBacktrack,  // Ignore this object's pointers.
       kAbort,      // Terminate the entire search immediately.
     };
     virtual ~Visitor() { }
     // Visits the object pointed to by *it. The iterator is only valid
-    // during this call. This method must not allocate from the heap.
+    // during this call. This method must not allocate from the heap or
+    // trigger GC in any way.
     virtual Direction VisitObject(StackIterator* it) = 0;
   };
 
-  // No GC is allowed during the lifetime of an ObjectGraph instance.
   explicit ObjectGraph(Isolate* isolate);
   ~ObjectGraph();
 
   // Visits all strongly reachable objects in the isolate's heap, in a
   // pre-order, depth first traversal.
   void IterateObjects(Visitor* visitor);
 
   // Like 'IterateObjects', but restricted to objects reachable from 'root'
   // (including 'root' itself).
   void IterateObjectsFrom(const Object& root, Visitor* visitor);
 
  private:
   Isolate* isolate_;

[Ivan Posva, 2014/05/05 17:22:38]

Now that this class is a StackResource you should be able to access the isolate
out of the resource avoiding the duplicated field here.

   DISALLOW_IMPLICIT_CONSTRUCTORS(ObjectGraph);
 };
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_GRAPH_H_