sync: Introduce ModelTypeRegistry and helpers

sync/engine/commit.h

Index: sync/engine/commit.h
diff --git a/sync/engine/commit.h b/sync/engine/commit.h
index 4750971bc7cb656545ecb998c764fe5845ae8e08..ab3e565058dbaca041af47d6f72fd683ea2034e4 100644
--- a/sync/engine/commit.h
+++ b/sync/engine/commit.h
@@ -9,8 +9,8 @@
 
 #include "base/stl_util.h"
 #include "sync/base/sync_export.h"
+#include "sync/engine/committer_list.h"
 #include "sync/engine/sync_directory_commit_contribution.h"
-#include "sync/engine/sync_directory_commit_contributor.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/engine/model_safe_worker.h"
 #include "sync/internal_api/public/util/syncer_error.h"
@@ -47,10 +47,11 @@ class SYNC_EXPORT_PRIVATE Commit {
 
   static Commit* Init(
       ModelTypeSet requested_types,
+      ModelTypeSet enabled_types,
       size_t max_entries,
       const std::string& account_name,
       const std::string& cache_guid,
-      CommitContributorMap* contributor_map,
+      CommitterList* committer_list,
       ExtensionsActivity* extensions_activity);
 
   SyncerError PostAndProcessResponse(