MenuButton: support Mac look & feel

ui/views/style/mac/combobox_background_mac.h

Index: ui/views/style/mac/combobox_background_mac.h
diff --git a/ui/views/style/mac/combobox_background_mac.h b/ui/views/style/mac/combobox_background_mac.h
index 5be50858d75f87e6c98a08ea52e3be7e80265fdc..ee752e81bad921bcb88b1d78fb256cc0364224c0 100644
--- a/ui/views/style/mac/combobox_background_mac.h
+++ b/ui/views/style/mac/combobox_background_mac.h
@@ -23,12 +23,15 @@ namespace views {
 // Mac look and feel.
 class ComboboxBackgroundMac : public Background {
  public:
-  ComboboxBackgroundMac();
+  // The |width| argument is the desired width of the "arrows" section from the
+  // diagram above.
+  ComboboxBackgroundMac(int width);

[tapted, 2016/04/21 06:06:46]

explicit. Also perhaps |width| -> |shoulder_width|? Or something better than
"shoulder" - my brain is struggling with this one, but `width` immediately makes
me think of the entire background width, which of course needs to come from the
view. The data member should change too.

[Elly Fong-Jones, 2016/04/21 15:30:27]

Done.

   ~ComboboxBackgroundMac() override;
 
   // Background:
   void Paint(gfx::Canvas* canvas, View* view) const override;
  private:

[tapted, 2016/04/21 06:06:46]

nit: blank line before

[Elly Fong-Jones, 2016/04/21 15:30:26]

Done.

+  int width_;
   DISALLOW_COPY_AND_ASSIGN(ComboboxBackgroundMac);
 };