[Squad] Get parent ComputedStyle from node, not from SVG layout object.

We currently don't compute style for elements being reattached in the
style recalc step when the element has custom style callbacks. The
reason is that some CustomStyleForLayoutObject() implementations rely on
ancestor elements being attached. Here, we stop relying on SVG
corresponding elements having a LayoutObject by retrieving ComputedStyle
from the Node instead. If the parent element is being (re-)attached, we
will get the non-attached style through Node::GetComputedStyle().

Bug: 813057
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I18b6a41087836746869071a409841692fa168537
Reviewed-on: https://chromium-review.googlesource.com/923732Reviewed-by: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537306}

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

@@ -34,6 +34,7 @@
 #include "core/css/resolver/StyleResolver.h"
 #include "core/dom/Document.h"
 #include "core/dom/ElementTraversal.h"
+#include "core/dom/NodeComputedStyle.h"
 #include "core/dom/ShadowRoot.h"
 #include "core/dom/events/Event.h"
 #include "core/frame/Settings.h"
@@ -1033,10 +1034,8 @@ scoped_refptr<ComputedStyle> SVGElement::CustomStyleForLayoutObject() {
     return GetDocument().EnsureStyleResolver().StyleForElement(this);
 
   const ComputedStyle* style = nullptr;
-  if (Element* parent = ParentOrShadowHostElement()) {
-    if (LayoutObject* layout_object = parent->GetLayoutObject())
-      style = layout_object->Style();
-  }
+  if (Element* parent = ParentOrShadowHostElement())
+    style = parent->GetComputedStyle();
 
   return GetDocument().EnsureStyleResolver().StyleForElement(
       CorrespondingElement(), style, style);