sync: Introduce ModelTypeRegistry and helpers

sync/sessions/sync_session_context.h

Index: sync/sessions/sync_session_context.h
diff --git a/sync/sessions/sync_session_context.h b/sync/sessions/sync_session_context.h
index 5995ab151dbcbba209872310ce532fcfa3030da7..f2025486727f5e6fe72b041b4410cfcc21f60cff 100644
--- a/sync/sessions/sync_session_context.h
+++ b/sync/sessions/sync_session_context.h
@@ -15,19 +15,15 @@
 #ifndef SYNC_SESSIONS_SYNC_SESSION_CONTEXT_H_
 #define SYNC_SESSIONS_SYNC_SESSION_CONTEXT_H_
 
-#include <map>
 #include <string>
 #include <vector>
 
-#include "base/stl_util.h"
 #include "sync/base/sync_export.h"
-#include "sync/engine/sync_directory_commit_contributor.h"
-#include "sync/engine/sync_directory_update_handler.h"
+#include "sync/engine/committer_list.h"
 #include "sync/engine/sync_engine_event.h"
-#include "sync/engine/syncer_types.h"
 #include "sync/engine/traffic_recorder.h"
+#include "sync/engine/updater_list.h"
 #include "sync/internal_api/public/engine/model_safe_worker.h"
-#include "sync/protocol/sync.pb.h"
 #include "sync/sessions/debug_info_getter.h"
 
 namespace syncer {
@@ -71,15 +67,7 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
     return enabled_types_;
   }
 
-  void set_routing_info(const ModelSafeRoutingInfo& routing_info);
-
-  UpdateHandlerMap* update_handler_map() {
-    return &update_handler_map_;
-  }
-
-  CommitContributorMap* commit_contributor_map() {
-    return &commit_contributor_map_;
-  }
+  void SetRoutingInfo(const ModelSafeRoutingInfo& routing_info);
 
   ExtensionsActivity* extensions_activity() {
     return extensions_activity_.get();
@@ -141,6 +129,14 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
     server_enabled_pre_commit_update_avoidance_ = value;
   }
 
+  UpdaterList* updater_list() {
+    return &updater_list_;
+  }
+
+  CommitterList* committer_list() {
+    return &committer_list_;
+  }
+
  private:
   // Rather than force clients to set and null-out various context members, we
   // extend our encapsulation boundary to scoped helpers that take care of this
@@ -156,24 +152,8 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
   // set_routing_info().
   ModelTypeSet enabled_types_;
 
-  // A map of 'update handlers', one for each enabled type.
-  // This must be kept in sync with the routing info.  Our temporary solution to
-  // that problem is to initialize this map in set_routing_info().
-  UpdateHandlerMap update_handler_map_;
-
-  // Deleter for the |update_handler_map_|.
-  STLValueDeleter<UpdateHandlerMap> update_handler_deleter_;
-
-  // A map of 'commit contributors', one for each enabled type.
-  // This must be kept in sync with the routing info.  Our temporary solution to
-  // that problem is to initialize this map in set_routing_info().
-  CommitContributorMap commit_contributor_map_;
-
-  // Deleter for the |commit_contributor_map_|.
-  STLValueDeleter<CommitContributorMap> commit_contributor_deleter_;
-
   // The set of ModelSafeWorkers.  Used to execute tasks of various threads.
-  std::map<ModelSafeGroup, scoped_refptr<ModelSafeWorker> > workers_;
+  std::vector<scoped_refptr<ModelSafeWorker> > workers_;
 
   // We use this to stuff extensions activity into CommitMessages so the server
   // can correlate commit traffic with extension-related bookmark mutations.
@@ -218,6 +198,10 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
   // enable the pre-commit update avoidance experiment described above.
   const bool client_enabled_pre_commit_update_avoidance_;
 
+  // Classes to manage the types hooked up to receive and commit sync data.
+  UpdaterList updater_list_;
+  CommitterList committer_list_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncSessionContext);
 };