sync: Introduce ModelTypeRegistry and helpers

sync/engine/commit_processor.cc

Index: sync/engine/commit_processor.cc
diff --git a/sync/engine/commit_processor.cc b/sync/engine/commit_processor.cc
new file mode 100644
index 0000000000000000000000000000000000000000..87e4c95cf03b7b7239379eee5ff9148259b16500
--- /dev/null
+++ b/sync/engine/commit_processor.cc
@@ -0,0 +1,52 @@
+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sync/engine/commit_processor.h"
+
+#include <map>
+
+#include "sync/engine/sync_directory_commit_contribution.h"
+#include "sync/engine/sync_directory_commit_contributor.h"
+#include "sync/protocol/sync.pb.h"
+
+namespace syncer {
+
+typedef std::map<ModelType, size_t> TypeToIndexMap;
+
+CommitProcessor::CommitProcessor(CommitContributorMap* commit_contributor_map)
+    : commit_contributor_map_(commit_contributor_map) {}
+
+CommitProcessor::~CommitProcessor() {}
+
+void CommitProcessor::GatherCommitContributions(
+    ModelTypeSet commit_types,
+    size_t max_entries,
+    ContributionMap* contributions) {
+  size_t num_entries = 0;
+  for (ModelTypeSet::Iterator it = commit_types.First();
+       it.Good(); it.Inc()) {
+    CommitContributorMap::iterator cm_it =
+        commit_contributor_map_->find(it.Get());
+    if (cm_it == commit_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) {
+      DCHECK_EQ(num_entries, max_entries)
+          << "Number of commit entries exceeeds maximum";
+      break;
+    }
+  }
+}
+
+}  // namespace syncer