[Smart Lock, Prefs reconciliation] Prefs migration logic for desktop platforms.

chrome/browser/password_manager/password_manager_setting_migrator_service.h

Index: chrome/browser/password_manager/password_manager_setting_migrator_service.h
diff --git a/chrome/browser/password_manager/password_manager_setting_migrator_service.h b/chrome/browser/password_manager/password_manager_setting_migrator_service.h
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index 0000000000000000000000000000000000000000..3399b85035b04c692d5e120d8b29b9381b0311e7
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+++ b/chrome/browser/password_manager/password_manager_setting_migrator_service.h
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+// Copyright (c) 2015 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_PASSWORD_MANAGER_PASSWORD_MANAGER_SETTING_MIGRATOR_SERVICE_H_
+#define CHROME_BROWSER_PASSWORD_MANAGER_PASSWORD_MANAGER_SETTING_MIGRATOR_SERVICE_H_
+
+#include <vector>
+
+#include "base/memory/singleton.h"
+#include "base/prefs/pref_change_registrar.h"
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "components/syncable_prefs/pref_service_syncable_observer.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+
+class Profile;
+
+namespace sync_driver {
+class SyncService;
+}
+
+// Service that is responsible for reconciling the legacy "Offer to save your
+// web passwords" setting (henceforth denoted 'L', for legacy) with the new
+// "Enable Smart Lock for Passwords" setting (henceforth denoted 'N', for new).
+//
+// It works as follows.
+//
+// Users who are not syncing (this is checked on start-up of the service
+// calling to SyncService:CanSyncStart()) are migrated on startup of the
+// service. These users can be in following states:
+//   1. N = 0, L = 0
+//   2. N = 1, L = 1
+//   3. N = 1, L = 0
+//   4. N = 0, L = 1
+//
+// Nothing should be done in case 1 and 2 since settings are already in sync;
+// in case 3,4 we change value of N to 0.
+//
+// For users who are syncing we save the values for the new and legacy
+// preference on service startup (|inital_values_|) and the values that come
+// from sync during models association step (|sync_data_|). Propagating change
+// of one preference to another preference without having this special treatment
+// will not always work. Here is an example which illustrates possible corner
+// case: the client executes the migration code for the first time, legacy
+// preference has a value 1, new preference was registered for the
+// first time and has default value which is also 1, the sync data snapshot
+// which user has on a client contains new preference equal to 0 and old
+// preference equal to 1, if we blindly propagate these values we first get
+// both preferences equal to 0 after priority pref model was associated and
+// then both preferences equal to 1 after preferences model was associated.
+// But the correct final value in this case is 0.
+//
+// At the end of model association step we derive the new values for both
+// settings using the following table (first column contains local values for
+// the preferences, first row contains values which came from sync, where _
+// means that the value did not come):
+//
+//  NL*  0_  1_  _0  _1  00  01  10  11
+//
+//  00   00  11  00  11  00  11  11  11
+//  01   x   x   x   x   00  00  00  11
+//  10   x   x   x   x   00  00  00  11
+//  11   00  11  00  11  00  00  00  11
+//
+// The service observes changes to both preferences (e.g. changes from sync,
+// changes from UI) and propagates the change to the other preference if needed.
+//
+// Note: componetization of this service currently is impossible, because it
+// depends on PrefServiceSyncable https://crbug.com/522536.
+class PasswordManagerSettingMigratorService
+    : public KeyedService,
+      public syncable_prefs::PrefServiceSyncableObserver,
+      public content::NotificationObserver {
+ public:
+  class Factory : public BrowserContextKeyedServiceFactory {
+   public:
+    static Factory* GetInstance();
+    static PasswordManagerSettingMigratorService* GetForProfile(
+        Profile* profile);
+
+   private:
+    friend struct base::DefaultSingletonTraits<Factory>;
+    friend class PasswordManagerSettingMigratorServiceTest;
+
+    Factory();
+    ~Factory() override;
+
+    // BrowserContextKeyedServiceFactory:
+    KeyedService* BuildServiceInstanceFor(
+        content::BrowserContext* profile) const override;
+    bool ServiceIsCreatedWithBrowserContext() const override;
+  };
+
+  explicit PasswordManagerSettingMigratorService(Profile* profile);
+  ~PasswordManagerSettingMigratorService() override;
+
+  void Shutdown() override;
+
+  // PrefServiceSyncableObserver:
+  void OnIsSyncingChanged() override;
+
+  // content::NotificationObserver:
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
+ private:
+  // Initializes the observers: preferences observers and sync status observers.
+  void InitObservers();
+
+  // Returns true if sync is expected to start for the user.
+  bool CanSyncStart();
+
+  // Called when the value of the |kCredentialsEnableService| preference
+  // changes, and updates the value of |kPasswordManagerSavingEnabled|
+  // preference accordingly.
+  void OnCredentialsEnableServicePrefChanged(
+      const std::string& changed_pref_name);
+
+  // Called when the value of the |kPasswordManagerSavingEnabled| preference
+  // changes, and updates the value of |kCredentialsEnableService| preference
+  // accordingly.
+  void OnPasswordManagerSavingEnabledPrefChanged(
+      const std::string& changed_pref_name);
+
+  // Turns off one pref if another pref is off.
+  void MigrateOffState(PrefService* prefs);
+
+  // Performs a migration after sync associates models. Migration is performed
+  // based on initial values for both preferences and values received from
+  // sync.
+  void MigrateAfterModelAssociation(PrefService* prefs);
+
+  // Contains values which have come from sync during model association step.
+  // The vector minimum size is 0 and the vector maximum size is 4:
+  //   * sync_data_ has length equal to 0, when no change to the preferences has
+  //   came from sync.
+  //   * sync_data has length equal to 1, when change to only one preference
+  //   came from sync and another pref already had this value, e.g local state
+  //   01 and N=1 came from sync.
+  //   * sync_data has length equals to 4, changes to both preference has came
+  //   from sync, e.g. local state is 11 and 01 came from sync.
+  // This way index 0 corresponds to kCredentialsEnableService, last index
+  // corresponds to kPasswordManagerSavingEnabled if size of sync_data_ equals
+  // to 4, otherwise the vector contains the value only for one preference.
+  std::vector<bool> sync_data_;
+
+  // The initial value for kCredentialsEnableService.
+  bool initial_new_pref_value_;
+  // The initial value for kPasswordManagerSavingEnabled.
+  bool initial_legacy_pref_value_;
+
+  Profile* const profile_;
+
+  sync_driver::SyncService* sync_service_;
+
+  PrefChangeRegistrar pref_change_registrar_;
+
+  // Used to register for notification that profile creation is complete.
+  content::NotificationRegistrar registrar_;
+
+  DISALLOW_COPY_AND_ASSIGN(PasswordManagerSettingMigratorService);
+};
+
+#endif  // CHROME_BROWSER_PASSWORD_MANAGER_PASSWORD_MANAGER_SETTING_MIGRATOR_SERVICE_H_