MenuButton: support Mac look & feel

ui/views/style/platform_style.h

 // Copyright 2015 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_STYLE_PLATFORM_STYLE_H_
 #define UI_VIEWS_STYLE_PLATFORM_STYLE_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 34 matching lines @@
   static std::unique_ptr<FocusableBorder> CreateComboboxBorder();
 
   // Creates the appropriate background for a Combobox.
   static std::unique_ptr<Background> CreateComboboxBackground();
 
   // Creates the default label button border for the given |style|. Used when a
   // custom default border is not provided for a particular LabelButton class.
   static std::unique_ptr<LabelButtonBorder> CreateLabelButtonBorder(
       Button::ButtonStyle style);
 
+  // Creates an ImageSkia containing the image to use for the menubutton arrow.
+  static gfx::ImageSkia CreateMenuButtonArrow(bool is_enabled);
+
+  // Create the appropriate background for a MenuButton.
+  static std::unique_ptr<Background> CreateMenuButtonBackground();
+
+  // Create the appropriate border for a MenuButton.
+  static std::unique_ptr<FocusableBorder> CreateMenuButtonBorder();
+
+  // A combobox or menubutton looks like this:
+  // ------------------------------------
+  // | text field ............. | arrow |
+  // ------------------------------------
+  // These functions return the width of the arrow part. This includes the arrow
+  // image itself as well as any padding on either side of it. On Mac, this is
+  // the width that will be filled by the arrow button's background, so text
+  // must not encroach upon it.
+  static int GetComboboxArrowWidth(Combobox::Style style);

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

At this point "shoulder" is really starting to grow on me :)

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

Done.

+  static int GetMenuButtonArrowWidth();
+
   // Creates the default scrollbar for the given orientation.
   static std::unique_ptr<ScrollBar> CreateScrollBar(bool is_horizontal);
 
   // Returns the current text color for the current button state.
   static SkColor TextColorForButton(const ButtonColorByState& color_by_state,
                                     const LabelButton& button);
 
   // Applies platform styles to |label| and fills |color_by_state| with the text
   // colors for normal, pressed, hovered, and disabled states, if the colors for
   // Button::STYLE_BUTTON buttons differ from those provided by ui::NativeTheme.
   static void ApplyLabelButtonTextStyle(Label* label,
                                         ButtonColorByState* color_by_state);
 
   // Applies the current system theme to the default border created by |button|.
   static std::unique_ptr<Border> CreateThemedLabelButtonBorder(
       LabelButton* button);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformStyle);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_STYLE_PLATFORM_STYLE_H_