Make CSSParserContext be garbage collected.

third_party/WebKit/Source/core/dom/CSSSelectorWatch.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 133 matching lines @@
   }
   return true;
 }
 
 void CSSSelectorWatch::watchCSSSelectors(const Vector<String>& selectors) {
   m_watchedCallbackSelectors.clear();
 
   StylePropertySet* callbackPropertySet =
       ImmutableStylePropertySet::create(nullptr, 0, UASheetMode);
 
+  CSSParserContext* context = CSSParserContext::create(UASheetMode);
   for (const auto& selector : selectors) {
-    CSSSelectorList selectorList = CSSParser::parseSelector(
-        CSSParserContext(UASheetMode, nullptr), nullptr, selector);
+    CSSSelectorList selectorList =
+        CSSParser::parseSelector(context, nullptr, selector);
     if (!selectorList.isValid())
       continue;
 
     // Only accept Compound Selectors, since they're cheaper to match.
     if (!allCompound(selectorList))
       continue;
 
     m_watchedCallbackSelectors.push_back(
         StyleRule::create(std::move(selectorList), callbackPropertySet));
   }
   supplementable()->styleEngine().watchedSelectorsChanged();
 }
 
 DEFINE_TRACE(CSSSelectorWatch) {
   visitor->trace(m_watchedCallbackSelectors);
   Supplement<Document>::trace(visitor);
 }
 
 }  // namespace blink