Do not leak when iterator outlives disk cache backend.

net/disk_cache/blockfile/rankings.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // See net/disk_cache/disk_cache.h for the public interface.
 
 #ifndef NET_DISK_CACHE_BLOCKFILE_RANKINGS_H_
 #define NET_DISK_CACHE_BLOCKFILE_RANKINGS_H_
 
 #include <list>
@@ skipping 76 matching lines @@
     }
 
    private:
     Rankings* rankings_;
     DISALLOW_COPY_AND_ASSIGN(ScopedRankingsBlock);
   };
 
   // If we have multiple lists, we have to iterate through all at the same time.
   // This structure keeps track of where we are on the iteration.
   struct Iterator {
-    explicit Iterator(Rankings* rankings);
-    ~Iterator();
+    Iterator();
+    void Reset();
 
     List list;                     // Which entry was returned to the user.
     CacheRankingsBlock* nodes[3];  // Nodes on the first three lists.
     Rankings* my_rankings;
   };
 
   Rankings();
   ~Rankings();
 
   bool Init(BackendImpl* backend, bool count_lists);
@@ skipping 96 matching lines @@
   BackendImpl* backend_;
   LruData* control_data_;  // Data related to the LRU lists.
   IteratorList iterators_;
 
   DISALLOW_COPY_AND_ASSIGN(Rankings);
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_BLOCKFILE_RANKINGS_H_