Rename RootWindowHost to WindowTreeHost

ui/aura/test/event_generator.cc

Index: ui/aura/test/event_generator.cc
diff --git a/ui/aura/test/event_generator.cc b/ui/aura/test/event_generator.cc
index d4a9c3a9c1f35f249516f8815a14a84d217f3673..b62d3a892eff8698cadc5a96b944a85a05cff807 100644
--- a/ui/aura/test/event_generator.cc
+++ b/ui/aura/test/event_generator.cc
@@ -587,8 +587,8 @@ void EventGenerator::DoDispatchEvent(ui::Event* event, bool async) {
     }
     pending_events_.push_back(pending_event);
   } else {
-    RootWindowHostDelegate* root_window_host_delegate =
-        current_root_window_->AsRootWindowHostDelegate();
+    WindowTreeHostDelegate* root_window_host_delegate =
+        current_root_window_->AsWindowTreeHostDelegate();
     if (event->IsKeyEvent()) {
       root_window_host_delegate->OnHostKeyEvent(
           static_cast<ui::KeyEvent*>(event));