Handle nested position:sticky elements correctly (compositor)

third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h

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 #ifndef WebLayerStickyPositionConstraint_h
 #define WebLayerStickyPositionConstraint_h
 
+#include "public/platform/WebLayer.h"
 #include "public/platform/WebPoint.h"
 #include "public/platform/WebRect.h"
 
 namespace blink {
 
 // TODO(flackr): Combine with WebLayerPositionConstraint.
 struct WebLayerStickyPositionConstraint {
   // True if the layer is sticky.
   bool isSticky : 1;
 
@@ skipping 16 matching lines @@
   WebPoint parentRelativeStickyBoxOffset;
 
   // The layout rectangle of the sticky element before it has been shifted
   // to stick.
   WebRect scrollContainerRelativeStickyBoxRect;
 
   // The layout rectangle of the containing block edges which this sticky
   // element should not be shifted beyond.
   WebRect scrollContainerRelativeContainingBlockRect;
 
+  // The nearest ancestor sticky layers that affect the sticky box constraint
+  // rect and the containing block constraint rect respectively.
+  int nearestLayerShiftingStickyBox;
+  int nearestLayerShiftingContainingBlock;
+
   WebLayerStickyPositionConstraint()
       : isSticky(false),
         isAnchoredLeft(false),
         isAnchoredRight(false),
         isAnchoredTop(false),
         isAnchoredBottom(false),
         leftOffset(0.f),
         rightOffset(0.f),
         topOffset(0.f),
-        bottomOffset(0.f) {}
+        bottomOffset(0.f),
+        nearestLayerShiftingStickyBox(WebLayer::kInvalidLayerId),
+        nearestLayerShiftingContainingBlock(WebLayer::kInvalidLayerId) {}
 };
 
 }  // namespace blink
 
 #endif  // WebLayerStickyPositionConstraint_h