Use the source display's pixel size as a mirror window's size.

ash/magnifier/magnification_controller.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/magnifier/magnification_controller.h"
 
-#include "ash/ash_root_window_transformer.h"
 #include "ash/display/display_controller.h"
 #include "ash/display/display_manager.h"
+#include "ash/display/root_window_transformers.h"
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/system/tray/system_tray_delegate.h"
 #include "base/synchronization/waitable_event.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/root_window_transformer.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_property.h"
 #include "ui/base/events/event.h"
@@ skipping 247 matching lines @@
   settings.AddObserver(this);
   settings.SetPreemptionStrategy(
       ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
   settings.SetTweenType(ui::Tween::EASE_OUT);
   settings.SetTransitionDuration(
       base::TimeDelta::FromMilliseconds(animate ? 100 : 0));
 
   gfx::Display display =
       Shell::GetScreen()->GetDisplayNearestWindow(root_window_);
   scoped_ptr<aura::RootWindowTransformer> transformer(
-      new AshRootWindowTransformer(root_window_, display));
+      internal::CreateRootWindowTransformerForDisplay(root_window_, display));
   root_window_->SetRootWindowTransformer(transformer.Pass());
 
   if (animate)
     is_on_animation_ = true;
 
   return true;
 }
 
 void MagnificationControllerImpl::EnsureRectIsVisibleWithScale(
     const gfx::Rect& target_rect,
@@ skipping 336 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationController:
 
 // static
 MagnificationController* MagnificationController::CreateInstance() {
   return new MagnificationControllerImpl();
 }
 
 }  // namespace ash