Use ScrollAnchor in FrameView and PaintLayerScrollableArea.

third_party/WebKit/Source/core/layout/LayoutBlock.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBlock.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlock.cpp b/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
index 884d88c7c867f4c4d64bfbc974ddf4acb98d2b54..ca0820104bca6e25983d581b066834c04425cd4b 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
@@ -897,6 +897,10 @@ void LayoutBlock::layout()
 {
     LayoutAnalyzer::Scope analyzer(*this);
 
+    bool needsScrollAnchoring = RuntimeEnabledFeatures::scrollAnchoringEnabled() && hasOverflowClip();
+    if (needsScrollAnchoring)
+        scrollableArea()->scrollAnchor().save();
+
     // Table cells call layoutBlock directly, so don't add any logic here.  Put code into
     // layoutBlock().
     layoutBlock(false);
@@ -907,6 +911,9 @@ void LayoutBlock::layout()
         clearLayoutOverflow();
 
     invalidateBackgroundObscurationStatus();
+
+    if (needsScrollAnchoring)
+        scrollableArea()->scrollAnchor().restore();
 }
 
 bool LayoutBlock::widthAvailableToChildrenHasChanged()