[Sync] Make BackendMigrator not wait for full sync cycles

chrome/browser/sync/backend_migrator.h

Index: chrome/browser/sync/backend_migrator.h
diff --git a/chrome/browser/sync/backend_migrator.h b/chrome/browser/sync/backend_migrator.h
index d3314aa94f0ff19674a04de6f9aac5c147a33683..1bffe2984a5e3dbb3642b03f3bfb61ee34205dd8 100644
--- a/chrome/browser/sync/backend_migrator.h
+++ b/chrome/browser/sync/backend_migrator.h
@@ -5,8 +5,10 @@
 #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"
@@ -15,20 +17,15 @@ 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|
     REENABLING_TYPES,   // Exit criteria: SYNC_CONFIGURE_DONE for enabled
                         // types.
   };
@@ -39,18 +36,23 @@ class BackendMigrator : public NotificationObserver,
   // 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;
+  // If in state WAITING_TO_START and ready to start, calls
+  // RestartMigration() (which advances the state).
+  void TryStartIfWaiting();
+
+  // Restarts migration, interrupting any existing migration.
+  void RestartMigration();
+
+  // Called by Observe().
+  void OnConfigureDone(const DataTypeManager::ConfigureResult& result);
 
   State state_;
   ProfileSyncService* service_;
@@ -58,10 +60,8 @@ class BackendMigrator : public NotificationObserver,
   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);
 };