Make CSSParserContext be garbage collected.

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

 // Copyright 2016 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/CSSPropertyAPIWebkitPadding.h"
 
 #include "core/css/parser/CSSParserContext.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 #include "core/css/parser/CSSPropertyParserHelpers.h"
 
 namespace blink {
 
 const CSSValue* CSSPropertyAPIWebkitPadding::parseSingleValue(
     CSSParserTokenRange& range,
-    const CSSParserContext& context) {
+    const CSSParserContext* context) {
   return consumeLengthOrPercent(
-      range, context.mode(), ValueRangeNonNegative,
+      range, context->mode(), ValueRangeNonNegative,
       CSSPropertyParserHelpers::UnitlessQuirk::Forbid);
 }
 
 }  // namespace blink