Implement the overflow-anchor CSS property as an opt-out for ScrollAnchoring

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
index 6284c867f468f7260b5e532761c1a86def250747..94998553c237f4f7d762068c5eb7d4e9b42a1978 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
@@ -278,6 +278,10 @@ public:
     virtual bool isPaintLayerScrollableArea() const { return false; }
     virtual bool isRootFrameViewport() const { return false; }
 
+    // Returns true if the scroller adjusts the scroll position to compensate
+    // for layout movements (bit.ly/scroll-anchoring).
+    virtual bool shouldPerformScrollAnchoring() const { return false; }
+
     // Need to promptly let go of owned animator objects.
     EAGERLY_FINALIZE();
     DECLARE_VIRTUAL_TRACE();