MacViews: Style BUTTON_STYLE buttons using the "modern" UI

ui/native_theme/native_theme_mac.h

 // Copyright (c) 2013 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_NATIVE_THEME_NATIVE_THEME_MAC_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_MAC_H_
 
 #include "base/macros.h"
 #include "ui/native_theme/native_theme_base.h"
 #include "ui/native_theme/native_theme_export.h"
 
 namespace ui {
 
 // Mac implementation of native theme support.
 class NATIVE_THEME_EXPORT NativeThemeMac : public NativeThemeBase {
  public:
   static const int kComboboxCornerRadius = 5;
 
+  // Type of gradient to use on a button background. Use HIGHLIGHTED for the
+  // default button of a window and all combobox controls, but only when the
+  // window is active.
+  enum class ButtonBackgroundType {
+    DISABLED,
+    HIGHLIGHTED,
+    NORMAL,
+    PRESSED,
+    COUNT
+  };
+
   static NativeThemeMac* instance();
 
   // Overridden from NativeTheme:
   SkColor GetSystemColor(ColorId color_id) const override;
 
   // Overridden from NativeThemeBase:
   void PaintMenuPopupBackground(
       SkCanvas* canvas,
       const gfx::Size& size,
       const MenuBackgroundExtraParams& menu_background) const override;
   void PaintMenuItemBackground(
       SkCanvas* canvas,
       State state,
       const gfx::Rect& rect,
       const MenuItemExtraParams& menu_item) const override;
 
   // Creates a shader appropriate for painting the background of a button.
-  static sk_sp<SkShader> GetButtonBackgroundShader(State state, int height);
+  static sk_sp<SkShader> GetButtonBackgroundShader(ButtonBackgroundType type,
+                                                   int height);
 
  private:
   NativeThemeMac();
   ~NativeThemeMac() override;
 
   DISALLOW_COPY_AND_ASSIGN(NativeThemeMac);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_MAC_H_