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

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 804 matching lines @@
     if (m_frame->isMainFrame() && !m_viewportScrollableArea) {
         ScrollableArea& visualViewport = m_frame->host()->visualViewport();
         ScrollableArea* layoutViewport = layoutViewportScrollableArea();
         DCHECK(layoutViewport);
         m_viewportScrollableArea = RootFrameViewport::create(visualViewport, *layoutViewport);
     }
 
     if (!m_scrollAnchor.hasScroller())
         m_scrollAnchor.setScroller(m_viewportScrollableArea ? m_viewportScrollableArea : this);
 
-    if (RuntimeEnabledFeatures::scrollAnchoringEnabled())
+    if (anchorScroll())
         m_scrollAnchor.save();
 }
 
 static inline void layoutFromRootObject(LayoutObject& root)
 {
     LayoutState layoutState(root);
     root.layout();
 }
 
 void FrameView::prepareLayoutAnalyzer()
@@ skipping 1278 matching lines @@
     if (layoutViewItem().isNull())
         return;
 
     scheduleUpdateWidgetsIfNecessary();
 
     if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
         scrollingCoordinator->notifyGeometryChanged();
 
     scrollToFragmentAnchor();
     // TODO(skobes): Figure out interactions between scroll anchor, fragment anchor, and history restoration.
-    if (RuntimeEnabledFeatures::scrollAnchoringEnabled())
+    if (anchorScroll())
         m_scrollAnchor.restore();
 
     sendResizeEventIfNeeded();
 }
 
 bool FrameView::wasViewportResized()
 {
     ASSERT(m_frame);
     LayoutViewItem layoutViewItem = this->layoutViewItem();
     if (layoutViewItem.isNull())
@@ skipping 1934 matching lines @@
 ScrollableArea* FrameView::layoutViewportScrollableArea()
 {
     Settings* settings = frame().settings();
     if (!settings || !settings->rootLayerScrolls())
         return this;
 
     LayoutViewItem layoutViewItem = this->layoutViewItem();
     return layoutViewItem.isNull() ? nullptr : layoutViewItem.getScrollableArea();
 }
 
-LayoutObject* FrameView::viewportLayoutObject()
+LayoutObject* FrameView::viewportLayoutObject() const
 {
     if (Document* document = frame().document()) {
         if (Element* element = document->viewportDefiningElement())
             return element->layoutObject();
     }
     return nullptr;
 }
 
 void FrameView::collectAnnotatedRegions(LayoutObject& layoutObject, Vector<AnnotatedRegionValue>& regions) const
 {
@@ skipping 168 matching lines @@
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(!layoutViewItem().isNull());
     return *layoutView();
 }
 
 } // namespace blink