[USS] Show USS counters in about:sync page

components/sync/driver/proxy_data_type_controller.cc

Index: components/sync/driver/proxy_data_type_controller.cc
diff --git a/components/sync/driver/proxy_data_type_controller.cc b/components/sync/driver/proxy_data_type_controller.cc
index 8188e38378db45eb8ebe8165c600333a8babf010..d3bf8f954a5c774a5c28c44e27ab62cee4237911 100644
--- a/components/sync/driver/proxy_data_type_controller.cc
+++ b/components/sync/driver/proxy_data_type_controller.cc
@@ -64,6 +64,12 @@ void ProxyDataTypeController::GetAllNodes(const AllNodesCallback& callback) {
   callback.Run(type(), base::MakeUnique<base::ListValue>());
 }
 
+void ProxyDataTypeController::GetStatusCounters(
+    const StatusCountersCallback& callback) {
+  syncer::StatusCounters counters;
+  callback.Run(type(), counters);
+}
+
 std::unique_ptr<DataTypeErrorHandler>
 ProxyDataTypeController::CreateErrorHandler() {
   NOTREACHED();