Refactor sync-specific parts out of SyncNotifier/SyncNotifierObserver

sync/notifier/sync_notifier.h

Index: sync/notifier/sync_notifier.h
diff --git a/sync/notifier/sync_notifier.h b/sync/notifier/sync_notifier.h
index 0c775f47277ce5a98085312f81a485d19655dadb..369ced1204fa3fd3fa03d0353757d9d046555734 100644
--- a/sync/notifier/sync_notifier.h
+++ b/sync/notifier/sync_notifier.h
@@ -12,6 +12,7 @@
 #include <string>
 
 #include "sync/internal_api/public/base/model_type.h"
+#include "sync/notifier/invalidation_util.h"
 
 namespace syncer {
 class SyncNotifierObserver;
@@ -21,8 +22,11 @@ class SyncNotifier {
   SyncNotifier() {}
   virtual ~SyncNotifier() {}
 
-  virtual void AddObserver(SyncNotifierObserver* observer) = 0;
-  virtual void RemoveObserver(SyncNotifierObserver* observer) = 0;
+  // Updates the set of ObjectIds associated with a given |handler|. Passing an
+  // empty ObjectIdSet will unregister |handler|. If two different handlers
+  // attempt to register for the same object ID, the first registration wins.
+  virtual void UpdateRegisteredIds(SyncNotifierObserver* handler,
+                                   const ObjectIdSet& ids) = 0;
 
   // SetUniqueId must be called once, before any call to
   // UpdateCredentials.  |unique_id| should be a non-empty globally
@@ -40,8 +44,6 @@ class SyncNotifier {
   virtual void UpdateCredentials(
       const std::string& email, const std::string& token) = 0;
 
-  virtual void UpdateEnabledTypes(ModelTypeSet enabled_types) = 0;
-
   // This is here only to support the old p2p notification implementation,
   // which is still used by sync integration tests.
   // TODO(akalin): Remove this once we move the integration tests off p2p