applyXSLTransform is too eager

Source/core/dom/StyleSheetCollection.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, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
@@ skipping 79 matching lines @@
 {
     if (document()->settings() && !document()->settings()->authorAndUserStylesEnabled())
         return;
 
     DocumentOrderedList::iterator begin = m_styleSheetCandidateNodes.begin();
     DocumentOrderedList::iterator end = m_styleSheetCandidateNodes.end();
     for (DocumentOrderedList::iterator it = begin; it != end; ++it) {
         Node* n = *it;
         StyleSheet* sheet = 0;
         CSSStyleSheet* activeSheet = 0;
-        if (n->nodeType() == Node::PROCESSING_INSTRUCTION_NODE) {
+        if (n->nodeType() == Node::PROCESSING_INSTRUCTION_NODE && !document()->isHTMLDocument()) {
             // Processing instruction (XML documents only).
             // We don't support linking to embedded CSS stylesheets, see <https://bugs.webkit.org/show_bug.cgi?id=49281> for discussion.
             ProcessingInstruction* pi = static_cast<ProcessingInstruction*>(n);
             // Don't apply XSL transforms to already transformed documents -- <rdar://problem/4132806>
             if (pi->isXSL() && !document()->transformSourceDocument()) {
                 // Don't apply XSL transforms until loading is finished.
-                if (!document()->parsing())
+                if (!document()->parsing() && !pi->isLoading())
                     document()->applyXSLTransform(pi);
                 return;
             }
             sheet = pi->sheet();
             if (sheet && !sheet->disabled() && sheet->isCSSStyleSheet())
                 activeSheet = static_cast<CSSStyleSheet*>(sheet);
         } else if ((n->isHTMLElement() && (n->hasTagName(linkTag) || n->hasTagName(styleTag))) || (n->isSVGElement() && n->hasTagName(SVGNames::styleTag))) {
             Element* e = toElement(n);
             AtomicString title = e->getAttribute(titleAttr);
             bool enabledViaScript = false;
@@ skipping 172 matching lines @@
         }
     }
     m_scopingNodesForStyleScoped.didRemoveScopingNodes();
     m_activeAuthorStyleSheets.swap(activeCSSStyleSheets);
     m_styleSheetsForStyleSheetList.swap(styleSheets);
 
     return requiresFullStyleRecalc;
 }
 
 }