Disable scroll anchoring if the user engages in a drag motion

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

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 815 matching lines @@
 
     if (shouldPerformScrollAnchoring())
         m_scrollAnchor.save();
 }
 
 bool FrameView::shouldPerformScrollAnchoring() const
 {
     return RuntimeEnabledFeatures::scrollAnchoringEnabled()
         && m_frame->settings() && !m_frame->settings()->rootLayerScrolls()
         && m_scrollAnchor.hasScroller()
-        && layoutBox()->style()->overflowAnchor() != AnchorNone;
+        && layoutBox()->style()->overflowAnchor() != AnchorNone
+        && !userMayHaveDragged();
 }
 
 static inline void layoutFromRootObject(LayoutObject& root)
 {
     LayoutState layoutState(root);
     root.layout();
 }
 
 void FrameView::prepareLayoutAnalyzer()
 {
@@ skipping 3436 matching lines @@
 }
 
 bool FrameView::canThrottleRendering() const
 {
     if (!RuntimeEnabledFeatures::renderingPipelineThrottlingEnabled())
         return false;
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 } // namespace blink