[Sync] Make BackendMigrator not wait for full sync cycles

chrome/browser/sync/backend_migrator.h

 // Copyright (c) 2011 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_SYNC_BACKEND_MIGRATOR_H_
 #define CHROME_BROWSER_SYNC_BACKEND_MIGRATOR_H_
 
+#include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
 #include "base/task.h"
-#include "chrome/browser/sync/profile_sync_service_observer.h"
+#include "chrome/browser/sync/glue/data_type_manager.h"
 #include "chrome/browser/sync/syncable/model_type.h"
 #include "content/common/notification_observer.h"
 #include "content/common/notification_registrar.h"
 
 class ProfileSyncService;
 
 namespace browser_sync {
 
-class DataTypeManager;
-
 // A class to perform migration of a datatype pursuant to the 'MIGRATION_DONE'
 // code in the sync protocol definition (protocol/sync.proto).
-class BackendMigrator : public NotificationObserver,
-                        public ProfileSyncServiceObserver {
+class BackendMigrator : public NotificationObserver {
  public:
   enum State {
     IDLE,
     WAITING_TO_START,   // Waiting for previous configuration to finish.
-    DISABLING_TYPES,    // Exit criteria: SYNC_CONFIGURE_DONE for enabled
-                        // types _excluding_ |to_migrate_|.
-    WAITING_FOR_PURGE,  // Exit criteria: SyncCycleEnded for enabled types
-                        // excluding |to_migrate|
+    DISABLING_TYPES,    // Exit criteria: SYNC_CONFIGURE_DONE for
+                        // enabled types _excluding_ |to_migrate_| and
+                        // empty download progress markers for types
+                        // in |to_migrate_|.
     REENABLING_TYPES,   // Exit criteria: SYNC_CONFIGURE_DONE for enabled
                         // types.
   };
 
   BackendMigrator(ProfileSyncService* service, DataTypeManager* manager);
   virtual ~BackendMigrator();
 
   // Starts a sequence of events that will disable and reenable |types|.
   void MigrateTypes(const syncable::ModelTypeSet& types);
 
-  // ProfileSyncServiceObserver implementation.
-  virtual void OnStateChanged();
-
   // NotificationObserver implementation.
   virtual void Observe(int type,
                        const NotificationSource& source,
-                       const NotificationDetails& details);
+                       const NotificationDetails& details) OVERRIDE;
 
   State state() const;
 
  private:
-  bool HasStartedMigrating() const;
+  // Must be called only in state WAITING_TO_START.  If ready to
+  // start, meaning the data type manager is configured, calls
+  // RestartMigration() and returns true.  Otherwise, does nothing and
+  // returns false.
+  bool TryStart();
+
+  // Restarts migration, interrupting any existing migration.
+  void RestartMigration();
+
+  // Called by Observe().
+  void OnConfigureDone(const DataTypeManager::ConfigureResult& result);
 
   State state_;
   ProfileSyncService* service_;
   DataTypeManager* manager_;
   NotificationRegistrar registrar_;
 
   syncable::ModelTypeSet to_migrate_;
-  bool restart_migration_;
 
-  // We use this to gracefully re-start migrations.
-  ScopedRunnableMethodFactory<BackendMigrator> method_factory_;
+  base::WeakPtrFactory<BackendMigrator> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BackendMigrator);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_BACKEND_MIGRATOR_H_