[Sync] Sync client should to exponential backoff when receive partial failure

components/sync/engine_impl/syncer_proto_util.cc

Index: components/sync/engine_impl/syncer_proto_util.cc
diff --git a/components/sync/engine_impl/syncer_proto_util.cc b/components/sync/engine_impl/syncer_proto_util.cc
index 9efd929169bc7425fe6ac591713d0e441813f31a..476ded98e016891f1ff40795c366b1ab8ffece3a 100644
--- a/components/sync/engine_impl/syncer_proto_util.cc
+++ b/components/sync/engine_impl/syncer_proto_util.cc
@@ -472,9 +472,15 @@ SyncerError SyncerProtoUtil::PostClientToServerMessage(
         DLOG(WARNING) << "Client fully throttled by syncer.";
         cycle->delegate()->OnThrottled(GetThrottleDelay(*response));
       } else {
+        // This is a special case, since server only throttle some of datatype,
+        // so can treat this case as partial failure.
         DLOG(WARNING) << "Some types throttled by syncer.";
         cycle->delegate()->OnTypesThrottled(
             sync_protocol_error.error_data_types, GetThrottleDelay(*response));
+        if (partial_failure_data_types != nullptr) {
+          *partial_failure_data_types = sync_protocol_error.error_data_types;
+        }
+        return SYNCER_OK;
       }
       return SERVER_RETURN_THROTTLED;
     case TRANSIENT_ERROR:
@@ -492,16 +498,17 @@ SyncerError SyncerProtoUtil::PostClientToServerMessage(
     case DISABLED_BY_ADMIN:
       return SERVER_RETURN_DISABLED_BY_ADMIN;
     case PARTIAL_FAILURE:
-      // This only happens when partial throttling during GetUpdates.
+      // This only happens when partial backoff during GetUpdates.
       if (!sync_protocol_error.error_data_types.Empty()) {
-        DLOG(WARNING) << "Some types throttled by syncer during GetUpdates.";
-        cycle->delegate()->OnTypesThrottled(
-            sync_protocol_error.error_data_types, GetThrottleDelay(*response));
+        DLOG(WARNING)
+            << "Some types got partial failure by syncer during GetUpdates.";
+        cycle->delegate()->OnTypesBackedOff(
+            sync_protocol_error.error_data_types);
       }
       if (partial_failure_data_types != nullptr) {
         *partial_failure_data_types = sync_protocol_error.error_data_types;
       }
-      return SERVER_RETURN_PARTIAL_FAILURE;
+      return SYNCER_OK;
     case CLIENT_DATA_OBSOLETE:
       return SERVER_RETURN_CLIENT_DATA_OBSOLETE;
     default: