Make CSSValuePool thread local to ensure correct parsing in colors on workers

third_party/WebKit/Source/web/WebCSSParser.cpp

 // Copyright 2015 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 "public/web/WebCSSParser.h"
 
 #include "core/css/parser/CSSParser.h"
 #include "public/platform/WebString.h"
 
 namespace blink {
 
 bool WebCSSParser::parseColor(WebColor* webColor, const WebString& colorString)
 {
     Color color = Color(*webColor);
-    bool success = CSSParser::parseColor(color, colorString, true);
+    bool success = CSSParser::parseColor(color, colorString, nullptr, true);
     *webColor = color.rgb();
     return success;
 }
 
 } // namespace blink