predictors: Version the resource_prefetch_predictor database.

chrome/browser/predictors/resource_prefetch_predictor_tables.h

 // Copyright 2014 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 CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_PREDICTOR_TABLES_H_
 #define CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_PREDICTOR_TABLES_H_
 
 #include <stddef.h>
 
 #include <map>
 #include <string>
 #include <vector>
 
+#include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "chrome/browser/predictors/predictor_table_base.h"
 #include "chrome/browser/predictors/resource_prefetch_common.h"
 #include "chrome/browser/predictors/resource_prefetch_predictor.pb.h"
 #include "content/public/common/resource_type.h"
 #include "net/base/request_priority.h"
 #include "url/gurl.h"
 
 namespace sql {
@@ skipping 100 matching lines @@
 
   // Deletes all data in all the tables.
   virtual void DeleteAllData();
 
   // The maximum length of the string that can be stored in the DB.
   static const size_t kMaxStringLength;
 
  private:
   friend class PredictorDatabaseInternal;
   friend class MockResourcePrefetchPredictorTables;
+  FRIEND_TEST_ALL_PREFIXES(ResourcePrefetchPredictorTablesTest,
+                           DatabaseVersionIsSet);
+  FRIEND_TEST_ALL_PREFIXES(ResourcePrefetchPredictorTablesTest,
+                           DatabaseIsResetWhenIncompatible);
 
   ResourcePrefetchPredictorTables();
   ~ResourcePrefetchPredictorTables() override;
 
   // Helper functions below help perform functions on the Url and host table
   // using the same code.
   void GetAllDataHelper(PrefetchKeyType key_type,
                         PrefetchDataMap* data_map,
                         std::vector<std::string>* to_delete);
   bool UpdateDataHelper(const PrefetchData& data);
   void DeleteDataHelper(PrefetchKeyType key_type,
                         const std::vector<std::string>& keys);
 
   // Returns true if the strings in the |data| are less than |kMaxStringLength|
   // in length.
   bool StringsAreSmallerThanDBLimit(const PrefetchData& data) const;
 
   // PredictorTableBase methods.
   void CreateTableIfNonExistent() override;
   void LogDatabaseStats() override;
 
-  bool DropTablesIfOutdated(sql::Connection* db);
+  // Database version. Always increment it when any change is made to the data
+  // schema (including the .proto).
+  static constexpr int kDatabaseVersion = 1;
+
+  static bool DropTablesIfOutdated(sql::Connection* db);
+  static int GetDatabaseVersion(sql::Connection* db);
+  static bool SetDatabaseVersion(sql::Connection* db, int version);
 
   // Helpers to return Statements for cached Statements. The caller must take
   // ownership of the return Statements.
   sql::Statement* GetUrlResourceDeleteStatement();
   sql::Statement* GetUrlResourceUpdateStatement();
   sql::Statement* GetUrlMetadataDeleteStatement();
   sql::Statement* GetUrlMetadataUpdateStatement();
 
   sql::Statement* GetHostResourceDeleteStatement();
   sql::Statement* GetHostResourceUpdateStatement();
   sql::Statement* GetHostMetadataDeleteStatement();
   sql::Statement* GetHostMetadataUpdateStatement();
 
   DISALLOW_COPY_AND_ASSIGN(ResourcePrefetchPredictorTables);
 };
 
 }  // namespace predictors
 
 #endif  // CHROME_BROWSER_PREDICTORS_RESOURCE_PREFETCH_PREDICTOR_TABLES_H_