[Sync] Convert SyncSessionSnapshot to a copy-able class.

chrome/browser/sync/backend_migrator.cc

 // 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.
 
 #include "chrome/browser/sync/backend_migrator.h"
 
 #include "base/message_loop.h"
 #include "base/string_number_conversions.h"
 #include "base/tracked_objects.h"
 #include "chrome/browser/sync/profile_sync_service.h"
 #include "chrome/common/chrome_notification_types.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_source.h"
 #include "sync/internal_api/configure_reason.h"
 #include "sync/internal_api/read_transaction.h"
 #include "sync/protocol/sync.pb.h"
 #include "sync/sessions/session_state.h"
 
 using syncable::ModelTypeSet;
 
 namespace browser_sync {
 
-using sessions::SyncSessionSnapshot;
 using syncable::ModelTypeToString;
 
 MigrationObserver::~MigrationObserver() {}
 
 BackendMigrator::BackendMigrator(const std::string& name,
                                  sync_api::UserShare* user_share,
                                  ProfileSyncService* service,
                                  DataTypeManager* manager,
                                  const base::Closure &migration_done_callback)
     : name_(name), user_share_(user_share), service_(service),
@@ skipping 196 matching lines @@
 syncable::ModelTypeSet
     BackendMigrator::GetPendingMigrationTypesForTest() const {
   return to_migrate_;
 }
 
 #undef SDVLOG
 
 #undef SLOG
 
 };  // namespace browser_sync