[sql] Consider fresh databases suitable for memory-mapped I/O.

content/browser/dom_storage/dom_storage_database.cc

 // Copyright 2013 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 "content/browser/dom_storage/dom_storage_database.h"
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "sql/statement.h"
@@ skipping 133 matching lines @@
     // If the file doesn't exist already and we haven't been asked to create
     // a file on disk, then we don't bother opening the database. This means
     // we wait until we absolutely need to put something onto disk before we
     // do so.
     return false;
   }
 
   db_.reset(new sql::Connection());
   db_->set_histogram_tag("DOMStorageDatabase");
 
+  // TODO(shess): The current mitigation for http://crbug.com/537742 stores
+  // state in the meta table, which this database does not use.
+  db_->set_mmap_disabled();
+
   if (file_path_.empty()) {
     // This code path should only be triggered by unit tests.
     if (!db_->OpenInMemory()) {
       NOTREACHED() << "Unable to open DOM storage database in memory.";
       failed_to_open_ = true;
       return false;
     }
   } else {
     if (!db_->Open(file_path_)) {
       LOG(ERROR) << "Unable to open DOM storage database at "
@@ skipping 120 matching lines @@
       CreateTableV2() &&
       CommitChanges(false, values) &&
       migration.Commit();
 }
 
 void DOMStorageDatabase::Close() {
   db_.reset(NULL);
 }
 
 }  // namespace content