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

ui/views/bubble/bubble_border.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 UI_VIEWS_BUBBLE_BUBBLE_BORDER_H_
 #define UI_VIEWS_BUBBLE_BUBBLE_BORDER_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/views/background.h"
 #include "ui/views/border.h"
 
 class SkPath;
+class SkRRect;
 
 namespace gfx {
 class Path;
 class Rect;
 }
 
 namespace views {
 class Painter;
 
 namespace internal {
@@ skipping 195 matching lines @@
   // The border and arrow stroke size used in image assets, in pixels.
   static const int kStroke;
 
   gfx::Size GetSizeForContentsSize(const gfx::Size& contents_size) const;
   gfx::ImageSkia* GetArrowImage() const;
   gfx::Rect GetArrowRect(const gfx::Rect& bounds) const;
   void GetArrowPathFromArrowBounds(const gfx::Rect& arrow_bounds,
                                    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_;
   int arrow_offset_;
   ArrowPaintType arrow_paint_type_;
   BubbleAlignment alignment_;
   Shadow shadow_;
   internal::BorderImages* images_;
   SkColor background_color_;
   bool use_theme_background_color_;
@@ skipping 12 matching lines @@
 
  private:
   BubbleBorder* border_;
 
   DISALLOW_COPY_AND_ASSIGN(BubbleBackground);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_BUBBLE_BUBBLE_BORDER_H_