Unify and provide one IsGarbageCollectedType<T> implementation.

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

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 51 matching lines @@
 class LayoutBox;
 class PaintLayer;
 class LayoutScrollbarPart;
 
 typedef WTF::HashMap<PaintLayer*, StickyPositionScrollingConstraints> StickyConstraintsMap;
 
 struct PaintLayerScrollableAreaRareData {
     WTF_MAKE_NONCOPYABLE(PaintLayerScrollableAreaRareData);
     USING_FAST_MALLOC(PaintLayerScrollableAreaRareData);
 public:
-    PaintLayerScrollableAreaRareData() {}
+    PaintLayerScrollableAreaRareData();
 
     StickyConstraintsMap m_stickyConstraintsMap;
 };
 
 // PaintLayerScrollableArea represents the scrollable area of a LayoutBox.
 //
 // To be scrollable, an element requires ‘overflow’ != visible. Note that this
 // doesn’t imply having scrollbars as you can always programmatically scroll
 // when ‘overflow’ is hidden (using JavaScript's element.scrollTo or
 // scrollLeft).
@@ skipping 372 matching lines @@
 #endif
 };
 
 DEFINE_TYPE_CASTS(PaintLayerScrollableArea, ScrollableArea, scrollableArea,
     scrollableArea->isPaintLayerScrollableArea(),
     scrollableArea.isPaintLayerScrollableArea());
 
 } // namespace blink
 
 #endif // LayerScrollableArea_h