sync: move invalidation version prefs out of SyncPrefs into InvalidatorStorage.

sync/notifier/non_blocking_invalidation_notifier.h

 // 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.
 //
 // An implementation of SyncNotifier that wraps InvalidationNotifier
 // on its own thread.
 
 #ifndef SYNC_NOTIFIER_NON_BLOCKING_INVALIDATION_NOTIFIER_H_
 #define SYNC_NOTIFIER_NON_BLOCKING_INVALIDATION_NOTIFIER_H_
 #pragma once
@@ skipping 12 matching lines @@
 #include "sync/util/weak_handle.h"
 
 namespace base {
 class MessageLoopProxy;
 }
 
 namespace sync_notifier {
 
 class NonBlockingInvalidationNotifier
     : public SyncNotifier,
+      // SyncNotifierObserver to "observe" our Core via WeakHandle.
       public SyncNotifierObserver {
  public:
   // |invalidation_state_tracker| must be initialized.
   NonBlockingInvalidationNotifier(
       const notifier::NotifierOptions& notifier_options,
       const InvalidationVersionMap& initial_max_invalidation_versions,
       const browser_sync::WeakHandle<InvalidationStateTracker>&
           invalidation_state_tracker,
       const std::string& client_info);
 
@@ skipping 31 matching lines @@
   scoped_refptr<Core> core_;
   scoped_refptr<base::MessageLoopProxy> parent_message_loop_proxy_;
   scoped_refptr<base::MessageLoopProxy> io_message_loop_proxy_;
 
   DISALLOW_COPY_AND_ASSIGN(NonBlockingInvalidationNotifier);
 };
 
 }  // namespace sync_notifier
 
 #endif  // SYNC_NOTIFIER_NON_BLOCKING_INVALIDATION_NOTIFIER_H_