Add a comma delimited syntax parser and use it for Accept-CH

Source/platform/CommaDelimitedParser.h

+// 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.
+
+#ifndef CommaDelimitedParser_h
+#define CommaDelimitedParser_h
+
+#include "platform/PlatformExport.h"
+#include "wtf/HashMap.h"
+#include "wtf/text/StringHash.h"
+
+namespace blink {
+
+class CommaDelimitedParser {
+public:
+    CommaDelimitedParser() { }
+    PLATFORM_EXPORT CommaDelimitedParser(String);
+
+    PLATFORM_EXPORT bool contains(String);
+
+private:
+    HashMap<String, bool, CaseFoldingHash> m_map;
+};
+
+} // namespace blink
+#endif
+