[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 44aef53949b15b5752bde550cbddc4db09d86254..463016edfbe447352b1c8b7191cc904c36cd8913 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<syncer::DataTypeErrorHandler>
 ProxyDataTypeController::CreateErrorHandler() {
   NOTREACHED();