Revert of Magnifier border is now more visible on light backgrounds.

ash/magnifier/partial_magnification_controller.h

 // 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.
 
 #ifndef ASH_MAGNIFIER_PARTIAL_MAGNIFICATION_CONTROLLER_H_
 #define ASH_MAGNIFIER_PARTIAL_MAGNIFICATION_CONTROLLER_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 29 matching lines @@
   // Switch PartialMagnified RootWindow to |new_root_window|. This does
   // following:
   //  - Remove the magnifier from the current root window.
   //  - Create a magnifier in the new root_window |new_root_window|.
   //  - Switch the target window from current window to |new_root_window|.
   void SwitchTargetRootWindowIfNeeded(aura::Window* new_root_window);
 
  private:
   friend class PartialMagnificationControllerTestApi;
 
-  class BorderRenderer;
   class ContentMask;
 
   // ui::EventHandler:
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnTouchEvent(ui::TouchEvent* event) override;
 
   // WindowObserver:
   void OnWindowDestroying(aura::Window* window) override;
 
   // WidgetObserver:
@@ skipping 29 matching lines @@
   // Masks the content of |border_layer_| so that only a circle outline is
   // drawn.
   std::unique_ptr<ContentMask> border_mask_;
 
   DISALLOW_COPY_AND_ASSIGN(PartialMagnificationController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_MAGNIFIER_PARTIAL_MAGNIFICATION_CONTROLLER_H_