Make Document::styleForElementIgnoringPendingStyleSheets() be aware of a flat tree structure

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 1974 matching lines @@
     updateStyleAndLayout();
 
     if (runPostLayoutTasks == RunPostLayoutTasksSynchronously && view())
         view()->flushAnyPendingPostLayoutTasks();
 }
 
 PassRefPtr<ComputedStyle> Document::styleForElementIgnoringPendingStylesheets(Element* element)
 {
     DCHECK_EQ(element->document(), this);
     StyleEngine::IgnoringPendingStylesheet ignoring(styleEngine());
-    return ensureStyleResolver().styleForElement(element, element->parentNode() ? element->parentNode()->ensureComputedStyle() : 0);
+    if (!element->canParticipateInFlatTree())
+        return ensureStyleResolver().styleForElement(element, nullptr);
+    ContainerNode* parent = LayoutTreeBuilderTraversal::parent(*element);
+    return ensureStyleResolver().styleForElement(element, parent ? parent->ensureComputedStyle() : nullptr);
+
 }
 
 PassRefPtr<ComputedStyle> Document::styleForPage(int pageIndex)
 {
     updateDistribution();
     return ensureStyleResolver().styleForPage(pageIndex);
 }
 
 bool Document::isPageBoxVisible(int pageIndex)
 {
@@ skipping 4034 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