[Sync] Rely on directory to decide which types need to be purged

sync/syncable/directory.h

 // Copyright 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.
 
 #ifndef SYNC_SYNCABLE_DIRECTORY_H_
 #define SYNC_SYNCABLE_DIRECTORY_H_
 
 #include <deque>
 #include <set>
 #include <string>
@@ skipping 91 matching lines @@
   // for) needs saved across runs of the application.
   struct SYNC_EXPORT_PRIVATE PersistedKernelInfo {
     PersistedKernelInfo();
     ~PersistedKernelInfo();
 
     // Set the |download_progress| entry for the given model to a
     // "first sync" start point.  When such a value is sent to the server,
     // a full download of all objects of the model will be initiated.
     void ResetDownloadProgress(ModelType model_type);
 
+    // Whether a valid progress marker exists for |model_type|.
+    bool HasEmptyDownloadProgress(ModelType model_type);
+
     // Last sync timestamp fetched from the server.
     sync_pb::DataTypeProgressMarker download_progress[MODEL_TYPE_COUNT];
     // Sync-side transaction version per data type. Monotonically incremented
     // when updating native model. A copy is also saved in native model.
     // Later out-of-sync models can be detected and fixed by comparing
     // transaction versions of sync model and native model.
     // TODO(hatiaol): implement detection and fixing of out-of-sync models.
     //                Bug 154858.
     int64 transaction_version[MODEL_TYPE_COUNT];
     // The store birthday we were given by the server. Contents are opaque to
@@ skipping 496 matching lines @@
   // are deleted in native models as well.
   scoped_ptr<DeleteJournal> delete_journal_;
 
   DISALLOW_COPY_AND_ASSIGN(Directory);
 };
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif // SYNC_SYNCABLE_DIRECTORY_H_