sync: Introduce ModelTypeRegistry and helpers

sync/engine/commit_processor.h

Index: sync/engine/commit_processor.h
diff --git a/sync/engine/commit_processor.h b/sync/engine/commit_processor.h
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+++ b/sync/engine/commit_processor.h
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+// 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.
+
+#ifndef SYNC_ENGINE_COMMIT_PROCESSOR_H_
+#define SYNC_ENGINE_COMMIT_PROCESSOR_H_
+
+#include <map>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "sync/base/sync_export.h"
+#include "sync/internal_api/public/base/model_type.h"
+#include "sync/internal_api/public/engine/model_safe_worker.h"
+#include "sync/sessions/model_type_registry.h"
+
+namespace syncer {
+
+namespace syncable {
+class Directory;
+}  // namespace syncable
+
+class SyncDirectoryCommitContributor;
+class SyncDirectoryCommitContribution;
+
+// This class manages the set of per-type committer objects.
+//
+// It owns these types and hides the details of iterating over all of them.
+// Many methods allow the caller to specify a subset of types on which the
+// operation is to be applied.  It is a logic error if the supplied set of types
+// contains a type which was not previously registered.
+class SYNC_EXPORT_PRIVATE CommitProcessor {
+ public:
+  typedef std::map<ModelType, SyncDirectoryCommitContribution*> ContributionMap;
+
+  explicit CommitProcessor(CommitContributorMap* commit_contributor_map);
+  ~CommitProcessor();
+
+  // Gathers a set of contributions to be used to populate a commit message.
+  void GatherCommitContributions(
+      ModelTypeSet commit_types,
+      size_t max_entries,
+      ContributionMap* contributions);
+
+ private:
+  // A map of 'commit contributors', one for each enabled type.
+  CommitContributorMap* commit_contributor_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(CommitProcessor);
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_COMMIT_PROCESSOR_H_