sync: Implement per-type commit interface

sync/engine/sync_directory_commit_contributor.cc

Index: sync/engine/sync_directory_commit_contributor.cc
diff --git a/sync/engine/sync_directory_commit_contributor.cc b/sync/engine/sync_directory_commit_contributor.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c8c6201607ef521dc89269506c4ebfc1f29ab46b
--- /dev/null
+++ b/sync/engine/sync_directory_commit_contributor.cc
@@ -0,0 +1,24 @@
+// Copyright (c) 2013 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/sync_directory_commit_contributor.h"
+
+#include "sync/engine/sync_directory_commit_contribution.h"
+
+namespace syncer {
+
+SyncDirectoryCommitContributor::SyncDirectoryCommitContributor(
+    syncable::Directory* dir,
+    ModelType type)
+    : dir_(dir),
+      type_(type) {}
+
+SyncDirectoryCommitContributor::~SyncDirectoryCommitContributor() {}
+
+SyncDirectoryCommitContribution*
+SyncDirectoryCommitContributor::GetContribution(size_t max_entries) {
+  return SyncDirectoryCommitContribution::Build(dir_, type_, max_entries);
+}
+
+}  // namespace syncer