ui: Cleanup class/struct forward declarations

ui/base/default_theme_provider.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_BASE_DEFAULT_THEME_PROVIDER_H_
 #define UI_BASE_DEFAULT_THEME_PROVIDER_H_
 
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "build/build_config.h"
 #include "ui/base/theme_provider.h"
 #include "ui/base/ui_base_export.h"
 
 namespace ui {
-class ResourceBundle;
-}
-
-namespace ui {
 
 class UI_BASE_EXPORT DefaultThemeProvider : public ThemeProvider {
  public:
   DefaultThemeProvider();
   ~DefaultThemeProvider() override;
 
   // Overridden from ui::ThemeProvider:
   gfx::ImageSkia* GetImageSkiaNamed(int id) const override;
   SkColor GetColor(int id) const override;
   color_utils::HSL GetTint(int id) const override;
@@ skipping 15 matching lines @@
   bool ShouldIncreaseContrast() const override;
 #endif
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DefaultThemeProvider);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_DEFAULT_THEME_PROVIDER_H_