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

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

Index: third_party/WebKit/Source/core/svg/SVGElement.cpp
diff --git a/third_party/WebKit/Source/core/svg/SVGElement.cpp b/third_party/WebKit/Source/core/svg/SVGElement.cpp
index 961d67e3d0c115786343754399437aa026e4dc1b..8c497432632b35efb52cb35d2f37182737232fcc 100644
--- a/third_party/WebKit/Source/core/svg/SVGElement.cpp
+++ b/third_party/WebKit/Source/core/svg/SVGElement.cpp
@@ -1029,11 +1029,8 @@ PassRefPtr<ComputedStyle> SVGElement::customStyleForLayoutObject() {
 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;
@@ -1041,6 +1038,17 @@ bool SVGElement::layoutObjectIsNeeded(const ComputedStyle& style) {
   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();