Clip scrollbars to box bounds when they don't fit.

third_party/WebKit/Source/core/paint/BoxClipper.h

 // Copyright 2014 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 BoxClipper_h
 #define BoxClipper_h
 
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "wtf/Allocator.h"
 
 namespace blink {
 
 class LayoutBox;
 struct PaintInfo;
 
-enum ContentsClipBehavior { ForceContentsClip, SkipContentsClipIfPossible };
+enum ContentsClipBehavior {
+    ForceContentsClip,
+    SkipContentsClipIfPossible,
+    ClipForScrollbars
+};
 
 class BoxClipper {
     STACK_ALLOCATED();
 public:
     BoxClipper(const LayoutBox&, const PaintInfo&, const LayoutPoint& accumulatedOffset, ContentsClipBehavior);
     ~BoxClipper();
 private:
     const LayoutBox& m_box;
     const PaintInfo& m_paintInfo;
     DisplayItem::Type m_clipType;
 };
 
 } // namespace blink
 
 #endif // BoxClipper_h