Refactor sync-specific parts out of SyncNotifier/SyncNotifierObserver

sync/notifier/sync_notifier_helper.h

Index: sync/notifier/sync_notifier_helper.h
diff --git a/sync/notifier/sync_notifier_helper.h b/sync/notifier/sync_notifier_helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..28ff187e6798228ec63f046a9176a02e49b9479e
--- /dev/null
+++ b/sync/notifier/sync_notifier_helper.h
@@ -0,0 +1,55 @@
+// 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.
+
+#ifndef SYNC_NOTIFIER_SYNC_NOTIFIER_HELPER_H_
+#define SYNC_NOTIFIER_SYNC_NOTIFIER_HELPER_H_
+
+#include <map>
+
+#include "base/basictypes.h"
+#include "base/observer_list.h"
+#include "sync/notifier/invalidation_util.h"
+#include "sync/notifier/object_id_payload_map.h"
+#include "sync/notifier/sync_notifier_observer.h"
+
+namespace syncer {
+
+// A helper class for classes that want to implement the SyncNotifier interface.
+// It helps keep track of registered handlers and which object ID registrations
+// are associated with which handlers, so implementors can just reuse the logic
+// here to dispatch invalidations and other interesting notifications.
+class SyncNotifierHelper {
+ public:
+  SyncNotifierHelper();
+  ~SyncNotifierHelper();
+
+  // Updates the set of ObjectIds associated with a given |handler|. Passing an
+  // empty ObjectIdSet will unregister |handler|. The return value is an
+  // ObjectIdSet containing values for all existing handlers.
+  ObjectIdSet UpdateRegisteredIds(SyncNotifierObserver* handler,
+                                  const ObjectIdSet& ids);
+
+  // Helper that sorts incoming invalidations into a bucket for each handler
+  // and then dispatches the batched invalidations to the corresponding handler.
+  void DispatchInvalidationsToHandlers(const ObjectIdPayloadMap& id_payloads,
+                                       IncomingNotificationSource source);
+
+  // Calls the given handler method for each handler that has registered IDs.
+  void EmitOnNotificationsEnabled();
+  void EmitOnNotificationsDisabled(NotificationsDisabledReason reason);
+
+ private:
+  typedef std::map<invalidation::ObjectId,
+                   SyncNotifierObserver*,
+                   ObjectIdLessThan> ObjectIdHandlerMap;
+
+  ObserverList<SyncNotifierObserver> handlers_;
+  ObjectIdHandlerMap id_to_handler_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncNotifierHelper);
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_NOTIFIER_SYNC_NOTIFIER_HELPER_H_