sync: Add interfaces for per-type sync

sync/engine/directory_commit_contributor.h

Index: sync/engine/directory_commit_contributor.h
diff --git a/sync/engine/sync_directory_commit_contributor.h b/sync/engine/directory_commit_contributor.h
similarity index 56%
rename from sync/engine/sync_directory_commit_contributor.h
rename to sync/engine/directory_commit_contributor.h
index 4a900754c00eeeed2f8a07f71670ee711c66f281..9bdfa4d1362f05c618751de19015d9267b70c6db 100644
--- a/sync/engine/sync_directory_commit_contributor.h
+++ b/sync/engine/directory_commit_contributor.h
@@ -2,17 +2,17 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef SYNC_ENGINE_SYNC_DIRECTORY_COMMIT_CONTRIBUTOR_H_
-#define SYNC_ENGINE_SYNC_DIRECTORY_COMMIT_CONTRIBUTOR_H_
+#ifndef SYNC_ENGINE_DIRECTORY_COMMIT_CONTRIBUTOR_H_
+#define SYNC_ENGINE_DIRECTORY_COMMIT_CONTRIBUTOR_H_
 
 #include <map>
 
+#include "sync/engine/commit_contributor.h"
+#include "sync/engine/directory_commit_contribution.h"
 #include "sync/internal_api/public/base/model_type.h"
 
 namespace syncer {
 
-class SyncDirectoryCommitContribution;
-
 namespace syncable {
 class Directory;
 }
@@ -23,13 +23,14 @@ class Directory;
 // Each instance of this class represents a particular type within the
 // syncable::Directory.  When asked, it will iterate through the directory, grab
 // any items of its type that are ready for commit, and return them in the form
-// of a SyncDirectoryCommitContribution.
-class SyncDirectoryCommitContributor {
+// of a DirectoryCommitContribution.
+class DirectoryCommitContributor : public CommitContributor {
  public:
-  SyncDirectoryCommitContributor(syncable::Directory* dir, ModelType type);
-  ~SyncDirectoryCommitContributor();
+  DirectoryCommitContributor(syncable::Directory* dir, ModelType type);
+  virtual ~DirectoryCommitContributor() OVERRIDE;
 
-  SyncDirectoryCommitContribution* GetContribution(size_t max_entries);
+  virtual DirectoryCommitContribution* GetContribution(
+      size_t max_entries) OVERRIDE;
 
  private:
   syncable::Directory* dir_;
@@ -38,4 +39,4 @@ class SyncDirectoryCommitContributor {
 
 }  // namespace
 
-#endif  // SYNC_ENGINE_SYNC_DIRECTORY_COMMIT_CONTRIBUTOR_H_
+#endif  // SYNC_ENGINE_DIRECTORY_COMMIT_CONTRIBUTOR_H_