When a font family pref changes to the empty string, pass it to WebKit.

chrome/common/pref_names_util.h

+// Copyright (c) 2012 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 CHROME_COMMON_PREF_NAMES_UTIL_H_
+#define CHROME_COMMON_PREF_NAMES_UTIL_H_
+
+#include <string>
+
+namespace pref_names_util {
+
+// Extracts the generic family and script from font name pref path |pref_path|.
+// For example, if |pref_path| is "webkit.webprefs.fonts.serif.Hang", returns
+// true and sets |generic_family| to "serif" and |script| to "Hang".
+bool ParseFontNamePrefPath(const std::string& pref_path,
+                           std::string* generic_family,
+                           std::string* script);
+
+}  // namespace pref_names_util
+
+#endif  // CHROME_COMMON_PREF_NAMES_UTIL_H_