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 562 matching lines @@
   }
 
   // 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 192 matching lines @@
                : nullptr;
   }
   bool HasAncestorWithClipPath() const {
     DCHECK(!needs_ancestor_dependent_compositing_inputs_update_);
     return has_ancestor_with_clip_path_;
   }
   bool HasDescendantWithClipPath() const {
     DCHECK(!needs_descendant_dependent_flags_update_);
     return has_descendant_with_clip_path_;
   }
+  bool HasDescendantThatSupportsSubsequenceCaching() const {
+    DCHECK(!needs_descendant_dependent_flags_update_);
+    return has_descendant_that_supports_subsequence_caching_;
+  }
 
   // Returns true if there is a descendant with blend-mode that is
   // not contained within another enclosing stacking context other
   // than the stacking context blend-mode creates, or the stacking
   // context this PaintLayer might create. This is needed because
   // blend-mode content needs to blend with the containing stacking
   // context's painted output, but not the content in any grandparent
   // stacking contexts.
   bool HasNonIsolatedDescendantWithBlendMode() const;
 
@@ skipping 112 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 273 matching lines @@
   unsigned needs_paint_phase_float_ : 1;
   unsigned previous_paint_phase_float_was_empty_ : 1;
   unsigned needs_paint_phase_descendant_block_backgrounds_ : 1;
   unsigned previous_paint_phase_descendant_block_backgrounds_was_empty_ : 1;
 
   // These bitfields are part of ancestor/descendant dependent compositing
   // inputs.
   unsigned has_descendant_with_clip_path_ : 1;
   unsigned has_non_isolated_descendant_with_blend_mode_ : 1;
   unsigned has_ancestor_with_clip_path_ : 1;
+  unsigned has_descendant_that_supports_subsequence_caching_ : 1;
 
   unsigned self_painting_status_changed_ : 1;
 
   LayoutBoxModelObject& layout_object_;
 
   PaintLayer* parent_;
   PaintLayer* previous_;
   PaintLayer* next_;
   PaintLayer* first_;
   PaintLayer* last_;
@@ skipping 38 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