Make CSSParserContext be garbage collected.

third_party/WebKit/Source/core/css/properties/CSSPropertyAPIZIndex.cpp

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/properties/CSSPropertyAPIZIndex.h"
 
 #include "core/css/parser/CSSPropertyParserHelpers.h"
 
 namespace blink {
 
 const CSSValue* CSSPropertyAPIZIndex::parseSingleValue(
     CSSParserTokenRange& range,
-    const CSSParserContext& context) {
+    const CSSParserContext* context) {
   if (range.peek().id() == CSSValueAuto)
     return CSSPropertyParserHelpers::consumeIdent(range);
   return CSSPropertyParserHelpers::consumeInteger(range);
 }
 
 }  // namespace blink