Have Document::elementSheet() return a reference

Source/core/css/parser/BisonCSSParser-in.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 1220 matching lines @@
     setupParser("@-internal-selector ", string, "");
 
     cssyyparse(this);
 
     m_selectorListForParseSelector = 0;
 }
 
 PassRefPtr<ImmutableStylePropertySet> BisonCSSParser::parseInlineStyleDeclaration(const String& string, Element* element)
 {
     Document& document = element->document();
-    CSSParserContext context = CSSParserContext(document.elementSheet()->contents()->parserContext(), UseCounter::getFrom(&document));
+    CSSParserContext context = CSSParserContext(document.elementSheet().contents()->parserContext(), UseCounter::getFrom(&document));
     context.setMode((element->isHTMLElement() && !document.inQuirksMode()) ? HTMLStandardMode : HTMLQuirksMode);
-    return BisonCSSParser(context).parseDeclaration(string, document.elementSheet()->contents());
+    return BisonCSSParser(context).parseDeclaration(string, document.elementSheet().contents());
 }
 
 PassRefPtr<ImmutableStylePropertySet> BisonCSSParser::parseDeclaration(const String& string, StyleSheetContents* contextStyleSheet)
 {
     setStyleSheet(contextStyleSheet);
 
     setupParser("@-internal-decls ", string, "");
     cssyyparse(this);
     m_rule = nullptr;
 
@@ skipping 8911 matching lines @@
 {
     // The tokenizer checks for the construct of an+b.
     // However, since the {ident} rule precedes the {nth} rule, some of those
     // tokens are identified as string literal. Furthermore we need to accept
     // "odd" and "even" which does not match to an+b.
     return equalIgnoringCase(token, "odd") || equalIgnoringCase(token, "even")
         || equalIgnoringCase(token, "n") || equalIgnoringCase(token, "-n");
 }
 
 }