Do not leak when iterator outlives disk cache backend.

net/disk_cache/blockfile/rankings.cc

 // 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.
 
 #include "net/disk_cache/blockfile/rankings.h"
 
 #include "base/metrics/histogram.h"
 #include "net/disk_cache/blockfile/backend_impl.h"
 #include "net/disk_cache/blockfile/disk_format.h"
 #include "net/disk_cache/blockfile/entry_impl.h"
@@ skipping 184 matching lines @@
 
 Rankings::ScopedRankingsBlock::ScopedRankingsBlock() : rankings_(NULL) {}
 
 Rankings::ScopedRankingsBlock::ScopedRankingsBlock(Rankings* rankings)
     : rankings_(rankings) {}
 
 Rankings::ScopedRankingsBlock::ScopedRankingsBlock(
     Rankings* rankings, CacheRankingsBlock* node)
     : scoped_ptr<CacheRankingsBlock>(node), rankings_(rankings) {}
 
-Rankings::Iterator::Iterator(Rankings* rankings) {
+Rankings::Iterator::Iterator() {
   memset(this, 0, sizeof(Iterator));
-  my_rankings = rankings;
 }
 
-Rankings::Iterator::~Iterator() {
-  for (int i = 0; i < 3; i++)
-    ScopedRankingsBlock(my_rankings, nodes[i]);
+void Rankings::Iterator::Reset() {
+  if (my_rankings) {
+    for (int i = 0; i < 3; i++)
+      ScopedRankingsBlock(my_rankings, nodes[i]);
+  }
+  memset(this, 0, sizeof(Iterator));
 }
 
 Rankings::Rankings() : init_(false) {}
 
 Rankings::~Rankings() {}
 
 bool Rankings::Init(BackendImpl* backend, bool count_lists) {
   DCHECK(!init_);
   if (init_)
     return false;
@@ skipping 693 matching lines @@
 void Rankings::DecrementCounter(List list) {
   if (!count_lists_)
     return;
 
   DCHECK(control_data_->sizes[list] > 0);
   if (control_data_->sizes[list] > 0)
     control_data_->sizes[list]--;
 }
 
 }  // namespace disk_cache