Have TreeScopeStyleSheetCollection::document() return a reference.

Source/core/dom/DocumentStyleSheetCollection.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 48 matching lines @@
     DocumentOrderedList::iterator begin = m_styleSheetCandidateNodes.begin();
     DocumentOrderedList::iterator end = m_styleSheetCandidateNodes.end();
     for (DocumentOrderedList::iterator it = begin; it != end; ++it) {
         Node* n = *it;
         StyleSheetCandidate candidate(*n);
 
         if (candidate.isXSL()) {
             // 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.
             // Don't apply XSL transforms to already transformed documents -- <rdar://problem/4132806>
-            if (RuntimeEnabledFeatures::xsltEnabled() && !document()->transformSourceDocument()) {
+            if (RuntimeEnabledFeatures::xsltEnabled() && !document().transformSourceDocument()) {
                 ProcessingInstruction* pi = toProcessingInstruction(n);
                 // Don't apply XSL transforms until loading is finished.
-                if (!document()->parsing() && !pi->isLoading())
-                    document()->applyXSLTransform(pi);
+                if (!document().parsing() && !pi->isLoading())
+                    document().applyXSLTransform(pi);
                 return;
             }
 
             continue;
         }
 
         if (candidate.isImport()) {
             Document* document = candidate.importedDocument();
             if (!document)
                 continue;
@@ skipping 15 matching lines @@
         if (candidate.hasPreferrableName(engine->preferredStylesheetSetName()))
             engine->selectStylesheetSetName(candidate.title());
         collector.appendSheetForList(sheet);
         if (candidate.canBeActivated(engine->preferredStylesheetSetName()))
             collector.appendActiveStyleSheet(toCSSStyleSheet(sheet));
     }
 }
 
 void DocumentStyleSheetCollection::collectStyleSheets(StyleEngine* engine, DocumentStyleSheetCollector& collector)
 {
-    ASSERT(document()->styleEngine() == engine);
+    ASSERT(document().styleEngine() == engine);
     collector.appendActiveStyleSheets(engine->injectedAuthorStyleSheets());
     collector.appendActiveStyleSheets(engine->documentAuthorStyleSheets());
     collectStyleSheetsFromCandidates(engine, collector);
 }
 
 bool DocumentStyleSheetCollection::updateActiveStyleSheets(StyleEngine* engine, StyleResolverUpdateMode updateMode)
 {
     StyleSheetCollection collection;
     ActiveDocumentStyleSheetCollector collector(collection);
     collectStyleSheets(engine, collector);
@@ skipping 24 matching lines @@
     m_scopingNodesForStyleScoped.didRemoveScopingNodes();
 
     collection.swap(*this);
 
     updateUsesRemUnits();
 
     return change.requiresFullStyleRecalc;
 }
 
 }