Unnecessary includes are also a layering violation.

Source/core/platform/ScrollbarThemeMacCommon.mm

 /*
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "core/platform/ScrollbarThemeMacCommon.h"
 
 #include <Carbon/Carbon.h>
-#include "core/frame/FrameView.h"
-#include "core/platform/ScrollView.h"
 #include "core/platform/ScrollbarThemeMacNonOverlayAPI.h"
 #include "core/platform/ScrollbarThemeMacOverlayAPI.h"
 #include "core/platform/graphics/Gradient.h"
 #include "core/platform/graphics/GraphicsContext.h"
 #include "core/platform/graphics/GraphicsContextStateSaver.h"
 #include "core/platform/graphics/GraphicsLayer.h"
 #include "core/platform/graphics/ImageBuffer.h"
 #include "core/platform/graphics/mac/ColorMac.h"
 #include "core/platform/mac/LocalCurrentGraphicsContext.h"
 #include "core/platform/mac/NSScrollerImpDetails.h"
 #include "core/platform/mac/ScrollAnimatorMac.h"
 #include "platform/PlatformMouseEvent.h"
+#include "platform/scroll/ScrollbarThemeClient.h"
 #include "public/platform/mac/WebThemeEngine.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebRect.h"
 #include "skia/ext/skia_utils_mac.h"
 #include "wtf/HashSet.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/TemporaryChange.h"
 #include "wtf/UnusedParam.h"
 
 // FIXME: There are repainting problems due to Aqua scroll bar buttons' visual overflow.
@@ skipping 341 matching lines @@
         case ForwardButtonEndPart:
             return kThemeBottomOutsideArrowPressed;
         case ThumbPart:
             return kThemeThumbPressed;
         default:
             return 0;
     }
 }
 
 } // namespace WebCore