Use ScrollAnchor in FrameView and PaintLayerScrollableArea.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
index ba6b5146cb375691b7c02983bac8fbf0de689151..dc54953a66ae681288b80527c072802a968e1453 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -46,6 +46,7 @@
 
 #include "core/CoreExport.h"
 #include "core/layout/LayoutBox.h"
+#include "core/layout/ScrollAnchor.h"
 #include "core/paint/PaintInvalidationCapableScrollableArea.h"
 #include "core/paint/PaintLayerFragment.h"
 #include "platform/heap/Handle.h"
@@ -333,6 +334,7 @@ public:
     IntRect rectForVerticalScrollbar(const IntRect& borderBoxRect) const;
 
     Widget* widget() override;
+    ScrollAnchor& scrollAnchor() { return m_scrollAnchor; }
     bool isPaintLayerScrollableArea() const override { return true; }
 
     DECLARE_VIRTUAL_TRACE();
@@ -374,6 +376,8 @@ private:
     // PaintInvalidationCapableScrollableArea
     LayoutBox& boxForScrollControlPaintInvalidation() const { return box(); }
 
+    bool scrollAnchoringEnabled() const;
+
     PaintLayer& m_layer;
 
     // Keeps track of whether the layer is currently resizing, so events can cause resizing to start and stop.
@@ -409,6 +413,8 @@ private:
     // LayoutObject to hold our custom resizer.
     LayoutScrollbarPart* m_resizer;
 
+    ScrollAnchor m_scrollAnchor;
+
 #if ENABLE(ASSERT)
     bool m_hasBeenDisposed;
 #endif