Create meta table atomically.

sql/meta_table.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.
 
 #ifndef SQL_META_TABLE_H_
 #define SQL_META_TABLE_H_
 #pragma once
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "sql/sql_export.h"
 
 namespace sql {
 
 class Connection;
 class Statement;
 
 class SQL_EXPORT MetaTable {
  public:
   MetaTable();
   ~MetaTable();
 
   // Returns true if the 'meta' table exists.
   static bool DoesTableExist(Connection* db);
 
   // Initializes the MetaTableHelper, creating the meta table if necessary. For
   // new tables, it will initialize the version number to |version| and the
-  // compatible version number to |compatible_version|.
+  // compatible version number to |compatible_version|.  Versions must be
+  // greater than 0 to distinguish missing versions (see GetVersionNumber()).
   bool Init(Connection* db, int version, int compatible_version);
 
   // Resets this MetaTable object, making another call to Init() possible.
   void Reset();
 
   // The version number of the database. This should be the version number of
   // the creator of the file. The version number will be 0 if there is no
   // previously set version number.
   //
   // See also Get/SetCompatibleVersionNumber().
@@ skipping 38 matching lines @@
   bool PrepareGetStatement(Statement* statement, const char* key);
 
   Connection* db_;
 
   DISALLOW_COPY_AND_ASSIGN(MetaTable);
 };
 
 }  // namespace sql
 
 #endif  // SQL_META_TABLE_H_