Remove most remaining sync/notifier dependencies

sync/notifier/invalidation_handler.h

Index: sync/notifier/invalidation_handler.h
diff --git a/sync/notifier/invalidation_handler.h b/sync/notifier/invalidation_handler.h
index a999cf6cb9e208edafae5b785feebfa0c51c1369..9cd41fe199b5cb1825e1fad93e4e3b4f7d6995dc 100644
--- a/sync/notifier/invalidation_handler.h
+++ b/sync/notifier/invalidation_handler.h
@@ -5,6 +5,8 @@
 #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"
 
@@ -14,6 +16,8 @@ class ObjectIdInvalidationMap;
 
 class SYNC_EXPORT InvalidationHandler {
  public:
+  InvalidationHandler();
+
   // Called when the invalidator state changes.
   virtual void OnInvalidatorStateChange(InvalidatorState state) = 0;
 
@@ -26,7 +30,7 @@ class SYNC_EXPORT InvalidationHandler {
   virtual std::string GetOwnerName() const = 0;
 
  protected:
-  virtual ~InvalidationHandler() {}
+  virtual ~InvalidationHandler();
 };
 
 }  // namespace syncer