Make GetRootWindow() return a Window instead of a RootWindow.

ash/display/root_window_transformers_unittest.cc

 // Copyright 2013 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/display/root_window_transformers.h"
 
 #include "ash/display/display_info.h"
 #include "ash/display/display_manager.h"
 #include "ash/launcher/launcher.h"
 #include "ash/magnifier/magnification_controller.h"
@@ skipping 78 matching lines @@
 
   float touch_radius_x() const { return touch_radius_x_; }
   float touch_radius_y() const { return touch_radius_y_; }
   float scroll_x_offset() const { return scroll_x_offset_; }
   float scroll_y_offset() const { return scroll_y_offset_; }
   float scroll_x_offset_ordinal() const { return scroll_x_offset_ordinal_; }
   float scroll_y_offset_ordinal() const { return scroll_y_offset_ordinal_; }
 
  private:
   gfx::Point mouse_location_;
-  aura::RootWindow* target_root_;
+  aura::Window* target_root_;
 
   float touch_radius_x_;
   float touch_radius_y_;
   float scroll_x_offset_;
   float scroll_y_offset_;
   float scroll_x_offset_ordinal_;
   float scroll_y_offset_ordinal_;
 
   DISALLOW_COPY_AND_ASSIGN(TestEventHandler);
 };
@@ skipping 294 matching lines @@
   EXPECT_EQ("0,125,0,125", transformer->GetHostInsets().ToString());
 
   UpdateDisplay("200x400,500x500");
   // The aspect ratio is flipped, so X margin is now 125.
   transformer = test_api.CreateCurrentRootWindowTransformer();
   EXPECT_EQ("125,0,125,0", transformer->GetHostInsets().ToString());
 }
 
 }  // namespace test
 }  // namespace ash