Be Careful when Accessing Map

chrome/browser/history/in_memory_url_index.cc

 // Copyright (c) 2011 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 "chrome/browser/history/in_memory_url_index.h"
 
 #include <algorithm>
 #include <functional>
 #include <iterator>
 #include <limits>
@@ skipping 394 matching lines @@
 InMemoryURLIndex::HistoryItemFactorGreater::HistoryItemFactorGreater(
     const HistoryInfoMap& history_info_map)
     : history_info_map_(history_info_map) {
 }
 
 InMemoryURLIndex::HistoryItemFactorGreater::~HistoryItemFactorGreater() {}
 
 bool InMemoryURLIndex::HistoryItemFactorGreater::operator()(
     const HistoryID h1,
     const HistoryID h2) {
-  const URLRow& r1(history_info_map_.find(h1)->second);
-  const URLRow& r2(history_info_map_.find(h2)->second);
+  HistoryInfoMap::const_iterator entry1(history_info_map_.find(h1));
+  if (entry1 == history_info_map_.end())
+    return false;
+  HistoryInfoMap::const_iterator entry2(history_info_map_.find(h2));
+  if (entry2 == history_info_map_.end())
+    return true;
+  const URLRow& r1(entry1->second);
+  const URLRow& r2(entry2->second);
   // First cut: typed count, visit count, recency.
   // TODO(mrossetti): This is too simplistic. Consider an approach which ranks
   // recently visited (within the last 12/24 hours) as highly important. Get
   // input from mpearson.
   if (r1.typed_count() != r2.typed_count())
     return (r1.typed_count() > r2.typed_count());
   if (r1.visit_count() != r2.visit_count())
     return (r1.visit_count() > r2.visit_count());
   return (r1.last_visit() > r2.last_visit());
 }
@@ skipping 701 matching lines @@
     if (iter->has_title()) {
       string16 title(UTF8ToUTF16(iter->title()));
       url_row.set_title(title);
     }
     private_data_->history_info_map_[history_id] = url_row;
   }
   return true;
 }
 
 }  // namespace history