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

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 1564 matching lines @@
     // and then trigger a full document recalc. We also need to clear it here since the
     // call to styleForElement on the body above can cache bad values for rem units if the
     // documentElement's style was dirty. We could keep track of which elements depend on
     // rem units like we do for viewport styles, but we assume root font size changes are
     // rare and just invalidate the cache for now.
     if (styleEngine().usesRemUnits() && (documentElement()->needsAttach() || !documentElement()->computedStyle() || documentElement()->computedStyle()->fontSize() != documentElementStyle->fontSize())) {
         ensureStyleResolver().invalidateMatchedPropertiesCache();
         documentElement()->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::FontSizeChange));
     }
 
+    EOverflowAnchor overflowAnchor = AnchorAuto;
     EOverflow overflowX = OverflowAuto;
     EOverflow overflowY = OverflowAuto;
     float columnGap = 0;
     if (overflowStyle) {
+        overflowAnchor = overflowStyle->overflowAnchor();
         overflowX = overflowStyle->overflowX();
         overflowY = overflowStyle->overflowY();
         // Visible overflow on the viewport is meaningless, and the spec says to treat it as 'auto':
         if (overflowX == OverflowVisible)
             overflowX = OverflowAuto;
         if (overflowY == OverflowVisible)
             overflowY = OverflowAuto;
+        if (overflowAnchor == AnchorVisible)
+            overflowAnchor = AnchorAuto;
         // Column-gap is (ab)used by the current paged overflow implementation (in lack of other
         // ways to specify gaps between pages), so we have to propagate it too.
         columnGap = overflowStyle->columnGap();
     }
 
     ScrollSnapType snapType = overflowStyle->getScrollSnapType();
     const LengthPoint& snapDestination = overflowStyle->scrollSnapDestination();
 
     RefPtr<ComputedStyle> documentStyle = layoutView()->mutableStyle();
     if (documentStyle->getWritingMode() != rootWritingMode
         || documentStyle->direction() != rootDirection
         || documentStyle->visitedDependentColor(CSSPropertyBackgroundColor) != backgroundColor
         || documentStyle->backgroundLayers() != backgroundLayers
         || documentStyle->imageRendering() != imageRendering
+        || documentStyle->overflowAnchor() != overflowAnchor
         || documentStyle->overflowX() != overflowX
         || documentStyle->overflowY() != overflowY
         || documentStyle->columnGap() != columnGap
         || documentStyle->getScrollSnapType() != snapType
         || documentStyle->scrollSnapDestination() != snapDestination) {
         RefPtr<ComputedStyle> newStyle = ComputedStyle::clone(*documentStyle);
         newStyle->setWritingMode(rootWritingMode);
         newStyle->setDirection(rootDirection);
         newStyle->setBackgroundColor(backgroundColor);
         newStyle->accessBackgroundLayers() = backgroundLayers;
         newStyle->setImageRendering(imageRendering);
+        newStyle->setOverflowAnchor(overflowAnchor);
         newStyle->setOverflowX(overflowX);
         newStyle->setOverflowY(overflowY);
         newStyle->setColumnGap(columnGap);
         newStyle->setScrollSnapType(snapType);
         newStyle->setScrollSnapDestination(snapDestination);
         layoutView()->setStyle(newStyle);
         setupFontBuilder(*newStyle);
     }
 
     if (body) {
@@ skipping 4413 matching lines @@
 }
 
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().getString().utf8().data());
 }
 #endif