sync: use progress markers instead of timestamps during GetUpdates

chrome/browser/sync/syncable/directory_backing_store.h

Index: chrome/browser/sync/syncable/directory_backing_store.h
diff --git a/chrome/browser/sync/syncable/directory_backing_store.h b/chrome/browser/sync/syncable/directory_backing_store.h
index e7ded8d9c86dda6d477fe893234482ff844a6332..7851e66efdb0f5126e07b5c22fa150833ae32858 100644
--- a/chrome/browser/sync/syncable/directory_backing_store.h
+++ b/chrome/browser/sync/syncable/directory_backing_store.h
@@ -81,6 +81,7 @@ class DirectoryBackingStore {
   FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, MigrateVersion71To72);
   FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, MigrateVersion72To73);
   FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, MigrateVersion73To74);
+  FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, MigrateVersion74To75);
   FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, ModelTypeIds);
   FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, Corruption);
   FRIEND_TEST_ALL_PREFIXES(DirectoryBackingStoreTest, DeleteEntries);
@@ -103,6 +104,7 @@ class DirectoryBackingStore {
   int CreateMetasTable(bool is_temporary);
   // Returns an sqlite return code, SQLITE_DONE on success.
   int CreateModelsTable();
+  int CreateV71ModelsTable();
 
   // We don't need to load any synced and applied deleted entries, we can
   // in fact just purge them forever on startup.
@@ -147,7 +149,7 @@ class DirectoryBackingStore {
   // the ModelType enum and the values we persist in the database to identify
   // a model.  We persist a default instance of the specifics protobuf as the
   // ID, rather than the enum value.
-  static ModelType ModelIdToModelTypeEnum(const string& model_id);
+  static ModelType ModelIdToModelTypeEnum(const void* data, int length);
   static string ModelTypeEnumToModelId(ModelType model_type);
 
   // Runs an integrity check on the current database.  If the
@@ -175,6 +177,7 @@ class DirectoryBackingStore {
   bool MigrateVersion71To72();
   bool MigrateVersion72To73();
   bool MigrateVersion73To74();
+  bool MigrateVersion74To75();
 
   // The handle to our sqlite on-disk store for initialization and loading, and
   // for saving changes periodically via SaveChanges, respectively.