Move preferred scrollbar style preference change listening from renderer to browser, 3 of 3.

Source/platform/scroll/ScrollbarThemeMacCommon.h

 /*
  * Copyright (C) 2008 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.
  */
 
 #ifndef ScrollbarThemeMacCommon_h
 #define ScrollbarThemeMacCommon_h
 
+#include "platform/mac/NSScrollerImpDetails.h"
 #include "platform/scroll/ScrollbarTheme.h"
 
 namespace WebCore {
 
 class PLATFORM_EXPORT ScrollbarThemeMacCommon : public ScrollbarTheme {
 public:
     virtual ~ScrollbarThemeMacCommon();
 
     virtual void registerScrollbar(ScrollbarThemeClient*) OVERRIDE;
     virtual void unregisterScrollbar(ScrollbarThemeClient*) OVERRIDE;
-    void preferencesChanged(float initialButtonDelay, float autoscrollButtonDelay, bool jumpOnTrackClick, bool redraw);
+    void preferencesChanged(float initialButtonDelay, float autoscrollButtonDelay, bool jumpOnTrackClick, NSScrollerStyle preferredScrollerStyle, bool redraw);
 
     virtual bool supportsControlTints() const OVERRIDE { return true; }
 
     virtual double initialAutoscrollTimerDelay() OVERRIDE;
     virtual double autoscrollTimerDelay() OVERRIDE;
 
     virtual void paintOverhangBackground(GraphicsContext*, const IntRect& horizontalOverhangArea, const IntRect& verticalOverhangArea, const IntRect& dirtyRect) OVERRIDE;
     virtual void paintOverhangShadows(GraphicsContext*, const IntSize& scrollOffset, const IntRect& horizontalOverhangArea, const IntRect& verticalOverhangArea, const IntRect& dirtyRect) OVERRIDE;
     virtual void paintTickmarks(GraphicsContext*, ScrollbarThemeClient*, const IntRect&) OVERRIDE;
 
+    static NSScrollerStyle recommendedScrollerStyle();
+
+    static bool isOverlayAPIAvailable();
+
 protected:
     virtual int maxOverlapBetweenPages() OVERRIDE { return 40; }
 
     virtual bool shouldCenterOnThumb(ScrollbarThemeClient*, const PlatformMouseEvent&) OVERRIDE;
     virtual bool shouldDragDocumentInsteadOfThumb(ScrollbarThemeClient*, const PlatformMouseEvent&) OVERRIDE;
     int scrollbarPartToHIPressedState(ScrollbarPart);
 
     virtual void updateButtonPlacement() { }
 
     void paintGivenTickmarks(GraphicsContext*, ScrollbarThemeClient*, const IntRect&, const Vector<IntRect>&);
 
     RefPtr<Pattern> m_overhangPattern;
 };
 
 }
 
 #endif // ScrollbarThemeMacCommon_h