Only store previous clip rects for PaintLayers that support subsequences.

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

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. 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>
@@ skipping 566 matching lines @@
   ScrollingCoordinator* GetScrollingCoordinator();
 
   // Returns true if the element or any ancestor is transformed.
   bool CompositesWithTransform() const;
 
   // Returns true if the element or any ancestor has non 1 opacity.
   bool CompositesWithOpacity() const;
 
   bool PaintsWithTransform(GlobalPaintFlags) const;
 
+  bool SupportsSubsequenceCaching() const;
+
   // Returns true if background phase is painted opaque in the given rect.
   // The query rect is given in local coordinates.
   bool BackgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const;
 
   bool ContainsDirtyOverlayScrollbars() const {
     return contains_dirty_overlay_scrollbars_;
   }
   void SetContainsDirtyOverlayScrollbars(bool dirty_scrollbars) {
     contains_dirty_overlay_scrollbars_ = dirty_scrollbars;
   }
@@ skipping 324 matching lines @@
   void SetPreviousScrollOffsetAccumulationForPainting(const IntSize& s) {
     previous_scroll_offset_accumulation_for_painting_ = s;
   }
 
   ClipRects* PreviousPaintingClipRects() const {
     return previous_painting_clip_rects_.Get();
   }
   void SetPreviousPaintingClipRects(ClipRects& clip_rects) {
     previous_painting_clip_rects_ = &clip_rects;
   }
+  void ClearPreviousPaintingClipRects() {
+    previous_painting_clip_rects_.Clear();
+  }
 
   LayoutRect PreviousPaintDirtyRect() const {
     return previous_paint_dirty_rect_;
   }
   void SetPreviousPaintDirtyRect(const LayoutRect& rect) {
     previous_paint_dirty_rect_ = rect;
   }
 
   PaintResult PreviousPaintResult() const {
     return static_cast<PaintResult>(previous_paint_result_);
@@ skipping 331 matching lines @@
 
 }  // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 CORE_EXPORT void showLayerTree(const blink::PaintLayer*);
 CORE_EXPORT void showLayerTree(const blink::LayoutObject*);
 #endif
 
 #endif  // Layer_h