Disable scroll anchoring if the user engages in a drag motion

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

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 252 matching lines @@
 void ScrollableArea::scrollPositionChanged(const DoublePoint& position, ScrollType scrollType)
 {
     TRACE_EVENT0("blink", "ScrollableArea::scrollPositionChanged");
 
     DoublePoint oldPosition = scrollPositionDouble();
     DoublePoint truncatedPosition = shouldUseIntegerScrollOffset() ? flooredIntPoint(position) : position;
 
     // Tell the derived class to scroll its contents.
     setScrollOffset(truncatedPosition, scrollType);
 
+    // If the scroll position is changed, the user is not dragging (e.g panning
+    // a map).
+    setUserMayHaveDragged(false);
+
     // Tell the scrollbars to update their thumb postions.
     // If the scrollbar does not have its own layer, it must always be
     // invalidated to reflect the new thumb position, even if the theme did not
     // invalidate any individual part.
     if (Scrollbar* horizontalScrollbar = this->horizontalScrollbar())
         horizontalScrollbar->offsetDidChange();
     if (Scrollbar* verticalScrollbar = this->verticalScrollbar())
         verticalScrollbar->offsetDidChange();
 
     if (scrollPositionDouble() != oldPosition) {
@@ skipping 330 matching lines @@
         std::max(0, size.height() - horizontalScrollbarHeight()));
 }
 
 DEFINE_TRACE(ScrollableArea)
 {
     visitor->trace(m_scrollAnimator);
     visitor->trace(m_programmaticScrollAnimator);
 }
 
 } // namespace blink