MacViews: For "NO_ASSET" MD bubbles, just use the border drawn by the window server.

ui/views/bubble/bubble_border.h

Index: ui/views/bubble/bubble_border.h
diff --git a/ui/views/bubble/bubble_border.h b/ui/views/bubble/bubble_border.h
index 181f5daee38a035677d9bec6f59f8cff23aa5dfa..ec1e25a88b5895e28593612c87c76494130f8dbc 100644
--- a/ui/views/bubble/bubble_border.h
+++ b/ui/views/bubble/bubble_border.h
@@ -15,6 +15,7 @@
 #include "ui/views/border.h"
 
 class SkPath;
+class SkRRect;
 
 namespace gfx {
 class Path;
@@ -230,8 +231,18 @@ class VIEWS_EXPORT BubbleBorder : public Border {
                                    SkPath* path) const;
   void DrawArrow(gfx::Canvas* canvas, const gfx::Rect& arrow_bounds) const;
 
+  // Returns the region within |view| representing the client area. This can be
+  // set as a canvas clip to ensure any fill or shadow from the border does not
+  // draw over the contents of the bubble.
+  SkRRect GetClientRect(const View& view) const;
+
+  // Paints an MD border. Ignores |shadow_|.
   void PaintMd(const View& view, gfx::Canvas* canvas);
 
+  // Paint for the NO_ASSETS shadow type. This just paints transparent pixels
+  // to make the window shape based on insets and GetBorderCornerRadius().
+  void PaintNoAssets(const View& view, gfx::Canvas* canvas);
+
   internal::BorderImages* GetImagesForTest() const;
 
   Arrow arrow_;