Remove mojo::String.

services/ui/ws/test_change_tracker.cc

Index: services/ui/ws/test_change_tracker.cc
diff --git a/services/ui/ws/test_change_tracker.cc b/services/ui/ws/test_change_tracker.cc
index b27a26a4def2ed338bf50d16972257a1ec1581bb..51ba96c2472fff88e4253ca74c7b2a337b0377ab 100644
--- a/services/ui/ws/test_change_tracker.cc
+++ b/services/ui/ws/test_change_tracker.cc
@@ -13,7 +13,6 @@
 #include "services/ui/common/util.h"
 
 using mojo::Array;
-using mojo::String;
 
 namespace ui {
 
@@ -376,7 +375,7 @@ void TestChangeTracker::OnPointerEventObserved(const ui::Event& event,
 }
 
 void TestChangeTracker::OnWindowSharedPropertyChanged(Id window_id,
-                                                      String name,
+                                                      const std::string& name,
                                                       Array<uint8_t> data) {
   Change change;
   change.type = CHANGE_TYPE_PROPERTY_CHANGED;