Remove most remaining sync/notifier dependencies

sync/notifier/invalidation_handler.h

 // Copyright 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.
 
 #ifndef SYNC_NOTIFIER_INVALIDATION_HANDLER_H_
 #define SYNC_NOTIFIER_INVALIDATION_HANDLER_H_
 
+#include <string>
+
 #include "sync/base/sync_export.h"
 #include "sync/internal_api/public/base/invalidator_state.h"
 
 namespace syncer {
 
 class ObjectIdInvalidationMap;
 
 class SYNC_EXPORT InvalidationHandler {
  public:
+  InvalidationHandler();
+
   // Called when the invalidator state changes.
   virtual void OnInvalidatorStateChange(InvalidatorState state) = 0;
 
   // Called when a invalidation is received.  The per-id states are in
   // |id_state_map| and the source is in |source|.  Note that this may be
   // called regardless of the current invalidator state.
   virtual void OnIncomingInvalidation(
       const ObjectIdInvalidationMap& invalidation_map) = 0;
 
   virtual std::string GetOwnerName() const = 0;
 
  protected:
-  virtual ~InvalidationHandler() {}
+  virtual ~InvalidationHandler();
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_NOTIFIER_INVALIDATION_HANDLER_H_