Move root_window_host* in aura to window_tree_host*.

ash/display/mirror_window_controller.cc

Index: ash/display/mirror_window_controller.cc
diff --git a/ash/display/mirror_window_controller.cc b/ash/display/mirror_window_controller.cc
index 07e5344de5506f22ae0ebd7cbb5279d5bb7576da..3637ad11aa981f1a104a096ddf748ce6a7527c7c 100644
--- a/ash/display/mirror_window_controller.cc
+++ b/ash/display/mirror_window_controller.cc
@@ -16,7 +16,7 @@
 #include "ash/display/display_info.h"
 #include "ash/display/display_manager.h"
 #include "ash/display/root_window_transformers.h"
-#include "ash/host/root_window_host_factory.h"
+#include "ash/host/window_tree_host_factory.h"
 #include "ash/root_window_settings.h"
 #include "ash/shell.h"
 #include "base/strings/stringprintf.h"
@@ -84,7 +84,7 @@ void MirrorWindowController::UpdateWindow(const DisplayInfo& display_info) {
   if (!root_window_.get()) {
     const gfx::Rect& bounds_in_native = display_info.bounds_in_native();
     aura::RootWindow::CreateParams params(bounds_in_native);
-    params.host = Shell::GetInstance()->root_window_host_factory()->
+    params.host = Shell::GetInstance()->window_tree_host_factory()->
         CreateWindowTreeHost(bounds_in_native);
     root_window_.reset(new aura::RootWindow(params));
     root_window_->window()->SetName(