Make CSSParserContext be garbage collected.

third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp

Index: third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp b/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
index 18fdb4e16d3c9244fc18f8e6441e74dfb26a6a8b..73226e8d9c7fbfd78ed0ce71f72b7febe00f8e7d 100644
--- a/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
+++ b/third_party/WebKit/Source/core/css/CSSKeyframesRule.cpp
@@ -99,7 +99,8 @@ void CSSKeyframesRule::appendRule(const String& ruleText) {
          m_keyframesRule->keyframes().size());
 
   CSSStyleSheet* styleSheet = parentStyleSheet();
-  CSSParserContext context(parserContext(), UseCounter::getFrom(styleSheet));
+  CSSParserContext* context =
+      CSSParserContext::create(parserContext(), styleSheet);
   StyleRuleKeyframe* keyframe = CSSParser::parseKeyframeRule(context, ruleText);
   if (!keyframe)
     return;