Disable scroll anchoring if the user engages in a drag motion

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

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
@@ skipping 604 matching lines @@
     // Viewport size that should be used for viewport units (i.e. 'vh'/'vw').
     FloatSize viewportSizeForViewportUnits() const;
 
     ScrollAnchor& scrollAnchor() { return m_scrollAnchor; }
     void clearScrollAnchor();
     bool shouldPerformScrollAnchoring() const override;
 
     // For PaintInvalidator temporarily. TODO(wangxianzhu): Move into PaintInvalidator.
     void invalidatePaintIfNeeded(const PaintInvalidationState&);
 
+    void setUserMayHaveDragged(bool dragged) override { m_userMayHaveDragged = dragged; }
+    bool userMayHaveDragged() const { return m_userMayHaveDragged; }
+
 protected:
     // Scroll the content via the compositor.
     bool scrollContentsFastPath(const IntSize& scrollDelta);
 
     // Scroll the content by invalidating everything.
     void scrollContentsSlowPath(const IntRect& updateRect);
 
     // These functions are used to create/destroy scrollbars.
     void setHasHorizontalScrollbar(bool);
     void setHasVerticalScrollbar(bool);
@@ skipping 298 matching lines @@
     bool m_needsScrollbarsUpdate;
     bool m_suppressAdjustViewSize;
     bool m_allowsLayoutInvalidationAfterLayoutClean;
 
     // For testing.
     struct ObjectPaintInvalidation {
         String name;
         PaintInvalidationReason reason;
     };
     std::unique_ptr<Vector<ObjectPaintInvalidation>> m_trackedObjectPaintInvalidations;
+
+    bool m_userMayHaveDragged;
 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count)
 {
     if (m_isVisuallyNonEmpty)
         return;
     m_visuallyNonEmptyCharacterCount += count;
     // Use a threshold value to prevent very small amounts of visible content from triggering didMeaningfulLayout.
     // The first few hundred characters rarely contain the interesting content of the page.
     static const unsigned visualCharacterThreshold = 200;
@@ skipping 11 matching lines @@
     if (m_visuallyNonEmptyPixelCount > visualPixelThreshold)
         setIsVisuallyNonEmpty();
 }
 
 DEFINE_TYPE_CASTS(FrameView, Widget, widget, widget->isFrameView(), widget.isFrameView());
 DEFINE_TYPE_CASTS(FrameView, ScrollableArea, scrollableArea, scrollableArea->isFrameView(), scrollableArea.isFrameView());
 
 } // namespace blink
 
 #endif // FrameView_h