sync: Add interfaces for per-type sync

sync/engine/commit_processor.h

 // Copyright 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;
+class CommitContributor;
+class CommitContribution;
 
 // 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;
+  typedef std::map<ModelType, CommitContribution*> ContributionMap;
 
+  // Contructs a CommitProcessor from a map of CommitContributors.
+  // The CommitProcessor does not own this map.
   explicit CommitProcessor(CommitContributorMap* commit_contributor_map);
   ~CommitProcessor();
 
   // Gathers a set of contributions to be used to populate a commit message.
+  //
+  // For each of the |commit_types| in this CommitProcessor's CommitContributor
+  // map, gather any entries queued for commit into CommitContributions.  The
+  // total number of entries in all the returned CommitContributions shall not
+  // exceed |max_entries|.
   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_