Gtk3: Refactor NativeThemeGtk3 to use foreign drawing only

chrome/browser/ui/libgtkui/native_theme_gtk3.h

 // Copyright 2016 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 CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK3_H_
 #define CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK3_H_
 
 #include "base/macros.h"
+#include "base/optional.h"
 #include "ui/native_theme/native_theme_base.h"
 
-typedef struct _GtkWidget GtkWidget;
-
 namespace libgtkui {
 
 // A version of NativeTheme that uses GTK3-rendered widgets.
 class NativeThemeGtk3 : public ui::NativeThemeBase {
  public:
   static NativeThemeGtk3* instance();
 
+  // Called when gtk theme changes.
+  void ResetColorCache();
+
   // Overridden from ui::NativeThemeBase:
   SkColor GetSystemColor(ColorId color_id) const override;
   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;
 
  private:
   NativeThemeGtk3();
   ~NativeThemeGtk3() override;
 
-  SkColor LookupGtkThemeColor(ColorId color_id) const;
-
-  // Returns various widgets for theming use.
-  // TODO(thomasanderson): Remove all of these.
-  GtkWidget* GetWindow() const;
-  GtkWidget* GetEntry() const;
-  GtkWidget* GetLabel() const;
-  GtkWidget* GetButton() const;
-  GtkWidget* GetBlueButton() const;
-  GtkWidget* GetTree() const;
-  GtkWidget* GetTooltip() const;
-  GtkWidget* GetMenu() const;
-  GtkWidget* GetMenuItem() const;
+  mutable base::Optional<SkColor> color_cache_[kColorId_NumColors];
 
   DISALLOW_COPY_AND_ASSIGN(NativeThemeGtk3);
 };
 
 }  // namespace libgtkui
 
 #endif  // CHROME_BROWSER_UI_LIBGTKUI_NATIVE_THEME_GTK3_H_