Unify SVG parent checks for LayoutObject construction using always the light tree parent.

third_party/WebKit/Source/core/svg/SVGElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Nikolas Zimmermann
  * <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2008 Rob Buis <buis@kde.org>
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Alp Toker <alp@atoker.com>
  * Copyright (C) 2009 Cameron McCormack <cam@mcc.id.au>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 1011 matching lines @@
       style = layoutObject->style();
   }
 
   return document().ensureStyleResolver().styleForElement(
       correspondingElement(), style, DisallowStyleSharing);
 }
 
 bool SVGElement::layoutObjectIsNeeded(const ComputedStyle& style) {
   // SVG elements only render when inside <svg>, or if the element is an <svg>
   // itself.
-  if (!isSVGSVGElement(*this)) {
-    ContainerNode* parent = FlatTreeTraversal::parent(*this);
-    if (!parent || !parent->isSVGElement())
-      return false;
-  }
+  if (!isSVGSVGElement(*this) && !isInSVGSubtree())

[fs, 2017/02/12 10:25:36]

Given that we have an override for SVGSVGElement already, we could consider
having that handle the isValid check (and delegate to the Element implementation
directly.) WDYT?

+    return false;
 
   if (!isValid())
     return false;
 
   return Element::layoutObjectIsNeeded(style);
 }
 
+bool SVGElement::isValidAndInSVGSubtree() const {
+  return isInSVGSubtree() && isValid();
+}
+
+bool SVGElement::isInSVGSubtree() const {

[fs, 2017/02/12 10:25:36]

Maybe "hasSVGParent" or "hasSVGAncestor" or something like that, because that is
closer to what the result is.

+  // Should we use the flat tree parent instead? If so, we should probably fix a
+  // few other checks.
+  return parentOrShadowHostElement() ||

[fs, 2017/02/12 10:25:35]

&&

+         parentOrShadowHostElement()->isSVGElement();
+}
+
 MutableStylePropertySet* SVGElement::animatedSMILStyleProperties() const {
   if (hasSVGRareData())
     return svgRareData()->animatedSMILStyleProperties();
   return nullptr;
 }
 
 MutableStylePropertySet* SVGElement::ensureAnimatedSMILStyleProperties() {
   return ensureSVGRareData()->ensureAnimatedSMILStyleProperties();
 }
 
@@ skipping 250 matching lines @@
   visitor->trace(m_className);
   Element::trace(visitor);
 }
 
 const AtomicString& SVGElement::eventParameterName() {
   DEFINE_STATIC_LOCAL(const AtomicString, evtString, ("evt"));
   return evtString;
 }
 
 }  // namespace blink