Client-side changes to support retry GU.

sync/protocol/sync.proto

Index: sync/protocol/sync.proto
diff --git a/sync/protocol/sync.proto b/sync/protocol/sync.proto
index ee051cdee592d200eab4160b83cef9f8de9f5f05..d5fc00c8616e13a5e6b2d8668fcf3f8bc0eeaf9a 100644
--- a/sync/protocol/sync.proto
+++ b/sync/protocol/sync.proto
@@ -584,10 +584,14 @@ message GetUpdatesMessage {
   // already created.  Should be set to true only by mobile clients.
   optional bool create_mobile_bookmarks_folder = 1000 [default = false];
 
-  // This value is an udpated version of the GetUpdatesCallerInfo's
+  // This value is an updated version of the GetUpdatesCallerInfo's
   // GetUpdatesSource.  It describes the reason for the GetUpdate request.
   // Introduced in M29.
   optional SyncEnums.GetUpdatesOrigin get_updates_origin = 9;
+
+  // Whether this GU also serves as a retry GU. Any GU that happens after
+  // retry timer timeout is a retry GU effectively.
+  optional bool is_retry = 10 [default = false];
 };
 
 message AuthenticateMessage {