Tie scroll anchoring adjustments to frame lifecycle instead of layout.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 60e26e7f06221dc65c16a6a16a84f84d02d69581..269315c8c8c2b9484cf5b7e4a151c033feff5db1 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -459,7 +459,7 @@ void PaintLayerScrollableArea::updateScrollOffset(const ScrollOffset& newOffset,
 
   // Clear the scroll anchor, unless it is the reason for this scroll.
   if (RuntimeEnabledFeatures::scrollAnchoringEnabled() &&
-      scrollType != AnchoringScroll)
+      scrollType != AnchoringScroll && scrollType != ClampingScroll)
     scrollAnchor()->clear();
 }
 
@@ -786,14 +786,10 @@ void PaintLayerScrollableArea::clampScrollOffsetsAfterLayout() {
     return;
   }
 
-  // Restore before clamping because clamping clears the scroll anchor.
-  if (shouldPerformScrollAnchoring())
-    m_scrollAnchor.restore();
-
   if (scrollOriginChanged())
     setScrollOffsetUnconditionally(clampScrollOffset(scrollOffset()));
   else
-    ScrollableArea::setScrollOffset(scrollOffset(), ProgrammaticScroll);
+    ScrollableArea::setScrollOffset(scrollOffset(), ClampingScroll);
 
   setNeedsScrollOffsetClamp(false);
   resetScrollOriginChanged();