[oilpan] Fix iterators over member collections to return Result<T>

Source/heap/Visitor.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 21 matching lines @@
 #define Visitor_h
 
 #include <wtf/Deque.h>
 #include <wtf/Forward.h>
 #include <wtf/HashTraits.h>
 #include <wtf/HashSet.h>
 
 namespace WebCore {
 
 template<typename T> class Member;
+template<typename T> class Result;
 
 #ifndef NDEBUG
 #define DECLARE_GC_TYPE_MARKER         \
 public:                                \
     static const char* s_gcTypeMarker; \
 private:                               \
 
 #define DEFINE_GC_TYPE_MARKER(type) const char* type::s_gcTypeMarker = #type
 #else
 #define DECLARE_GC_TYPE_MARKER
@@ skipping 59 matching lines @@
     void visit(const Member<T>& t)
     {
         if (!t)
             return;
 #ifndef NDEBUG
         AcceptTrait<T>::check(this, t.raw());
 #endif
         AcceptTrait<T>::visit(this, t.raw());
     }
 
+    // Result version of the one-argument templated visit method. This is used
+    // for visiting collections: The iterator returns Result<T> and  we visit
+    // them. This visitor method is befriended by Result<T> which allows it to
+    // use releaseRaw.
+    template<typename T>
+    void visit(const Result<T>& t)
+    {
+        if (!t)
+            return;
+#ifndef NDEBUG
+        AcceptTrait<T>::check(this, t.releaseRaw());
+#endif
+        AcceptTrait<T>::visit(this, t.releaseRaw());
+    }
+
     template<typename T, size_t N>
     void visit(const Vector<Member<T>, N>& vector)
     {
         for (typename Vector<Member<T>, N>::const_iterator it = vector.begin(); it != vector.end(); ++it)
             visit(*it);
     }
 
     template<typename T>
     void visit(const HashSet<Member<T> >& hashSet)
     {
@@ skipping 151 matching lines @@
 public:
     virtual void accept(Visitor*) = 0;
     virtual ~HeapVisitable()
     {
     }
 };
 
 }
 
 #endif