Magnifier border is now more visible on light backgrounds.

ash/magnifier/partial_magnification_controller.h

Index: ash/magnifier/partial_magnification_controller.h
diff --git a/ash/magnifier/partial_magnification_controller.h b/ash/magnifier/partial_magnification_controller.h
index 3a7cf0fdcf926f886e6eace327832679857520a5..b6f5dc32ad788eba3744d82b974fcbb090802596 100644
--- a/ash/magnifier/partial_magnification_controller.h
+++ b/ash/magnifier/partial_magnification_controller.h
@@ -47,6 +47,7 @@ class ASH_EXPORT PartialMagnificationController : public ui::EventHandler,
  private:
   friend class PartialMagnificationControllerTestApi;
 
+  class BorderRenderer;
   class ContentMask;
 
   // ui::EventHandler:
@@ -84,6 +85,8 @@ class ASH_EXPORT PartialMagnificationController : public ui::EventHandler,
   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