Fix NULL deref in HistoryBackend::ExpireHistoryBetween.

chrome/browser/history/history_backend.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 "chrome/browser/history/history_backend.h"
 
 #include <algorithm>
 #include <functional>
 #include <list>
 #include <map>
@@ skipping 692 matching lines @@
     thumbnail_db_->TrimMemory(trim_aggressively);
   if (archived_db_)
     archived_db_->TrimMemory(trim_aggressively);
 }
 
 void HistoryBackend::CloseAllDatabases() {
   if (db_) {
     // Commit the long-running transaction.
     db_->CommitTransaction();
     db_.reset();
+    // Forget the first recorded time since the database is closed.
+    first_recorded_time_ = base::Time();
   }
   if (thumbnail_db_) {
     thumbnail_db_->CommitTransaction();
     thumbnail_db_.reset();
   }
   if (archived_db_) {
     archived_db_->CommitTransaction();
     archived_db_.reset();
   }
 }
@@ skipping 1755 matching lines @@
   db_->GetStartDate(&first_recorded_time_);
   // Force a commit, if the user is deleting something for privacy reasons, we
   // want to get it on disk ASAP.
   Commit();
 }
 
 void HistoryBackend::ExpireHistoryBetween(
     const std::set<GURL>& restrict_urls,
     Time begin_time,
     Time end_time) {
-  if (db_) {
-    if (begin_time.is_null() && (end_time.is_null() || end_time.is_max()) &&
-        restrict_urls.empty()) {
-      // Special case deleting all history so it can be faster and to reduce the
-      // possibility of an information leak.
-      DeleteAllHistory();
-    } else {
-      // Clearing parts of history, have the expirer do the depend
-      expirer_.ExpireHistoryBetween(restrict_urls, begin_time, end_time);
+  if (!db_)
+    return;
 
-      // Force a commit, if the user is deleting something for privacy reasons,
-      // we want to get it on disk ASAP.
-      Commit();
-    }
+  if (begin_time.is_null() && (end_time.is_null() || end_time.is_max()) &&
+      restrict_urls.empty()) {
+    // Special case deleting all history so it can be faster and to reduce the
+    // possibility of an information leak.
+    DeleteAllHistory();
+  } else {
+    // Clearing parts of history, have the expirer do the depend
+    expirer_.ExpireHistoryBetween(restrict_urls, begin_time, end_time);
+
+    // Force a commit, if the user is deleting something for privacy reasons,
+    // we want to get it on disk ASAP.
+    Commit();
   }
 
   if (begin_time <= first_recorded_time_)
     db_->GetStartDate(&first_recorded_time_);
 }
 
 void HistoryBackend::ExpireHistoryForTimes(
     const std::set<base::Time>& times,
     base::Time begin_time, base::Time end_time) {
   if (times.empty() || !db_)
@@ skipping 347 matching lines @@
   int rank = kPageVisitStatsMaxTopSites;
   std::map<GURL, int>::const_iterator it = most_visited_urls_map_.find(url);
   if (it != most_visited_urls_map_.end())
     rank = (*it).second;
   UMA_HISTOGRAM_ENUMERATION("History.TopSitesVisitsByRank",
                             rank, kPageVisitStatsMaxTopSites + 1);
 }
 #endif
 
 }  // namespace history