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 c5ef7b90586085ef7cd3f9fad0d78cc727581450..83691b8b2a5b1467e59f4bee882dd28c06d63e57 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -584,6 +584,8 @@ 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;
@@ -928,6 +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_;