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 24c59a018c4f8126ef6a7f0457cae941a6597a47..1cbabee56ef273667ece1978e098a45581043a59 100644
--- a/sync/notifier/sync_notifier.h
+++ b/sync/notifier/sync_notifier.h
@@ -21,8 +21,9 @@ class SyncNotifier {
   SyncNotifier() {}
   virtual ~SyncNotifier() {}
 
-  virtual void AddObserver(SyncNotifierObserver* observer) = 0;
-  virtual void RemoveObserver(SyncNotifierObserver* observer) = 0;
+  virtual void AddHandler(SyncNotifierObserver* observer) = 0;
+  virtual void RemoveHandler(SyncNotifierObserver* observer) = 0;
+  virtual void ReloadHandlers() = 0;

[akalin, 2012/07/11 00:10:24]

I know ReloadHandlers was in my design doc.  It was to batch registrations to
tango, but Daniel added a comment saying that we shouldn't have to worry about
it, since registrations are batched anyway.  So now I'm not sure if I still like
it.

We could have something like just:

virtual void AddHandler(ObjectId, Observer*);
virtual void RemoveHandler(ObjectId, Observer*);

instead.  Or maybe with set<ObjectId> instead.  Or map<ObjectId, Observer*>. 
What do you think?

[dcheng, 2012/07/11 05:45:28]

Add/Remove would push some of the diffing logic to each of the handlers, which I
think would be cleaner to avoid. I'll see what I can hack together for something
like SyncNotifier::UpdateHandledIds(Observer*, ObjectIdSet) though.

 
   // SetUniqueId must be called once, before any call to
   // UpdateCredentials.  |unique_id| should be a non-empty globally
@@ -40,8 +41,6 @@ class SyncNotifier {
   virtual void UpdateCredentials(
       const std::string& email, const std::string& token) = 0;
 
-  virtual void UpdateEnabledTypes(syncer::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