Use ScrollAnchor in FrameView and PaintLayerScrollableArea.

third_party/WebKit/Source/core/frame/FrameView.h

Index: third_party/WebKit/Source/core/frame/FrameView.h
diff --git a/third_party/WebKit/Source/core/frame/FrameView.h b/third_party/WebKit/Source/core/frame/FrameView.h
index 6521e00896bfc22057d122dc02b3d1d1113f00d2..e0b2be76f5cc1b19775872eba12f8a86c57448cd 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -31,6 +31,7 @@
 #include "core/frame/LayoutSubtreeRootList.h"
 #include "core/frame/RootFrameViewport.h"
 #include "core/layout/LayoutAnalyzer.h"
+#include "core/layout/ScrollAnchor.h"
 #include "core/paint/PaintInvalidationCapableScrollableArea.h"
 #include "core/paint/PaintPhase.h"
 #include "platform/RuntimeEnabledFeatures.h"
@@ -585,6 +586,8 @@ public:
     // Viewport size that should be used for viewport units (i.e. 'vh'/'vw').
     FloatSize viewportSizeForViewportUnits() const;
 
+    ScrollAnchor& scrollAnchor() { return m_scrollAnchor; }
+
 protected:
     // Scroll the content via the compositor.
     bool scrollContentsFastPath(const IntSize& scrollDelta);
@@ -756,6 +759,8 @@ private:
     LayoutBox& boxForScrollControlPaintInvalidation() const override;
     LayoutScrollbarPart* resizer() const override { return nullptr; }
 
+    bool scrollAnchoringEnabled() const;
+
     LayoutSize m_size;
 
     typedef HashSet<RefPtr<LayoutEmbeddedObject>> EmbeddedObjectSet;
@@ -896,6 +901,7 @@ private:
     RefPtr<ClipPaintPropertyNode> m_contentClip;
 
     bool m_isUpdatingAllLifecyclePhases;
+    ScrollAnchor m_scrollAnchor;
 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count)