sync: Introduce ModelTypeRegistry and helpers

sync/engine/commit.cc

Index: sync/engine/commit.cc
diff --git a/sync/engine/commit.cc b/sync/engine/commit.cc
index a8db1a41ee3821cad3572ad1b044b88075306410..665f709118d5144ae8c3ebaa0fd9030fdcac7b02 100644
--- a/sync/engine/commit.cc
+++ b/sync/engine/commit.cc
@@ -30,34 +30,18 @@ Commit::~Commit() {
 
 Commit* 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) {
   // Gather per-type contributions.
   ContributionMap contributions;
-  size_t num_entries = 0;
-  for (ModelTypeSet::Iterator it = requested_types.First();
-       it.Good(); it.Inc()) {
-    CommitContributorMap::iterator cm_it = contributor_map->find(it.Get());
-    if (cm_it == contributor_map->end()) {
-      NOTREACHED()
-          << "Could not find requested type " << ModelTypeToString(it.Get())
-          << " in contributor map.";
-      continue;
-    }
-    size_t spaces_remaining = max_entries - num_entries;
-    SyncDirectoryCommitContribution* contribution =
-        cm_it->second->GetContribution(spaces_remaining);
-    if (contribution) {
-      num_entries += contribution->GetNumEntries();
-      contributions.insert(std::make_pair(it.Get(), contribution));
-    }
-    if (num_entries == max_entries) {
-      break;  // No point in continuting to iterate in this case.
-    }
-  }
+  committer_list->GatherCommitContributions(
+      requested_types,
+      max_entries,
+      &contributions);
 
   // Give up if no one had anything to commit.
   if (contributions.empty())
@@ -81,13 +65,9 @@ Commit* Commit::Init(
   }
 
   // Set the client config params.
-  ModelTypeSet enabled_types;
-  for (CommitContributorMap::iterator it = contributor_map->begin();
-       it != contributor_map->end(); ++it) {
-    enabled_types.Put(it->first);
-  }
-  commit_util::AddClientConfigParamsToMessage(enabled_types,
-                                                    commit_message);
+  commit_util::AddClientConfigParamsToMessage(
+      enabled_types,
+      commit_message);
 
   // Finally, serialize all our contributions.
   for (std::map<ModelType, SyncDirectoryCommitContribution*>::iterator it =