Introdcue AshWindowTreeHost and move ash/chrome specific code in WTH to ash.

ash/magnifier/magnification_controller.cc

Index: ash/magnifier/magnification_controller.cc
diff --git a/ash/magnifier/magnification_controller.cc b/ash/magnifier/magnification_controller.cc
index dd3b0d8bca32f02440fdd952e1f4762ad278925c..5d2ed1a518aa8c402addd9c109cb1034bb43c69d 100644
--- a/ash/magnifier/magnification_controller.cc
+++ b/ash/magnifier/magnification_controller.cc
@@ -7,13 +7,14 @@
 #include "ash/accelerators/accelerator_controller.h"
 #include "ash/accessibility_delegate.h"
 #include "ash/ash_switches.h"
+#include "ash/host/ash_window_tree_host.h"
 #include "ash/display/root_window_transformers.h"
+#include "ash/host/root_window_transformer.h"
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray_delegate.h"
 #include "base/command_line.h"
 #include "base/synchronization/waitable_event.h"
 #include "ui/aura/client/cursor_client.h"
-#include "ui/aura/root_window_transformer.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_property.h"
 #include "ui/aura/window_tree_host.h"
@@ -270,9 +271,9 @@ bool MagnificationControllerImpl::RedrawDIP(const gfx::PointF& position_in_dip,
 
   gfx::Display display =
       Shell::GetScreen()->GetDisplayNearestWindow(root_window_);
-  scoped_ptr<aura::RootWindowTransformer> transformer(
+  scoped_ptr<RootWindowTransformer> transformer(
       internal::CreateRootWindowTransformerForDisplay(root_window_, display));
-  root_window_->GetHost()->SetRootWindowTransformer(transformer.Pass());
+  AshWindowTreeHost::Get(root_window_)->SetRootWindowTransformer(transformer.Pass());
 
   if (animate)
     is_on_animation_ = true;