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 17 matching lines @@
   bool is_active_ = false;
 
   // The host widget is the root parent for all of the layers. The widget's
   // location follows the mouse, which causes the layers to also move.
   views::Widget* host_widget_ = nullptr;
 
   // Draws the background with a zoom filter applied.
   std::unique_ptr<ui::Layer> zoom_layer_;
   // Draws an outline that is overlayed on top of |zoom_layer_|.
   std::unique_ptr<ui::Layer> border_layer_;
+  // Draws a multicolored black/white/black border on top of |border_layer_|.
+  std::unique_ptr<BorderRenderer> border_renderer_;

[James Cook, 2016/09/16 01:48:52]

optional: Consider documenting that this must be destroyed before
|border_layer_|.  (Otherwise the layer will have a pointer to a deleted
delegate.)  Things are destroyed in the correct order here due to the member
order, but it might be nice to point out that that isn't an accident.

[sammiequon, 2016/09/16 16:33:35]

Done.

   // Masks the content of |zoom_layer_| so that only a circle is magnified.
   std::unique_ptr<ContentMask> zoom_mask_;
   // 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_