Only store previous clip rects for PaintLayers that support subsequences.

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index 3c9991421b30bf38c06f3e770bc203bebae249b6..c0944a535a1a2f877ef5acf4e7602e4dcb71c926 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -580,6 +580,8 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
 
   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;
@@ -792,6 +794,10 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
     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
@@ -924,6 +930,9 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
   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_;
@@ -1217,6 +1226,7 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
   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;