ui: Cleanup class/struct forward declarations

ui/base/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_THEME_PROVIDER_H_
 #define UI_BASE_THEME_PROVIDER_H_
 
 #include "build/build_config.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/layout.h"
 #include "ui/base/ui_base_export.h"
 
 #if defined(OS_MACOSX)
 #ifdef __OBJC__
 @class NSColor;
 @class NSGradient;
 @class NSImage;
 #else
 class NSColor;
 class NSGradient;
 class NSImage;
 #endif  // __OBJC__
 #endif  // OS_*
 
-class SkBitmap;
-
 namespace base {
 class RefCountedMemory;
 }
 
 namespace color_utils {
 struct HSL;
 }
 
 namespace gfx {
 class ImageSkia;
@@ skipping 73 matching lines @@
   virtual NSGradient* GetNSGradient(int id) const = 0;
 
   // Whether the "increase contrast" accessibility setting is enabled.
   virtual bool ShouldIncreaseContrast() const = 0;
 #endif
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_THEME_PROVIDER_H_