sync: Implement NonBlockingTypeProcessorCore

sync/engine/non_blocking_sync_common.h

Index: sync/engine/non_blocking_sync_common.h
diff --git a/sync/engine/non_blocking_sync_common.h b/sync/engine/non_blocking_sync_common.h
index f07fdb2684e2c2239bc9f838456e06242bd8234f..d0e0f9d03863c5ba06cca8887454e9d657f6db09 100644
--- a/sync/engine/non_blocking_sync_common.h
+++ b/sync/engine/non_blocking_sync_common.h
@@ -14,6 +14,8 @@
 
 namespace syncer {
 
+static const int64 kUncommittedVersion = -1;
+
 // Data-type global state that must be accessed and updated on the sync thread,
 // but persisted on or through the model thread.
 struct SYNC_EXPORT_PRIVATE DataTypeState {
@@ -43,6 +45,11 @@ struct SYNC_EXPORT_PRIVATE DataTypeState {
   // client-tagged data types supported by non-blocking sync, but we will
   // continue to emulate the directory sync's behavior for now.
   int64 next_client_id;
+
+  // This flag is set to true when the first download cycle is complete.  The
+  // NonBlockingTypeProcessor should not attempt to commit any items until this
+  // flag is set.
+  bool initial_sync_done;
 };
 
 struct SYNC_EXPORT_PRIVATE CommitRequestData {