Remove 'String::append' from some of the blink source.

Source/platform/Language.cpp

 /*
  * Copyright (C) 2010, 2013 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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 #include "config.h"
 #include "platform/Language.h"
 
 #include "public/platform/Platform.h"
-#include "wtf/text/WTFString.h"
+#include "wtf/text/StringBuilder.h"
 
 namespace WebCore {
 
 static String platformLanguage()
 {
-    DEFINE_STATIC_LOCAL(String, computedDefaultLanguage, ());
+    DEFINE_STATIC_LOCAL(StringBuilder, computedDefaultLanguage, ());
     if (computedDefaultLanguage.isEmpty()) {
         computedDefaultLanguage.append(blink::Platform::current()->defaultLocale());
         ASSERT(!computedDefaultLanguage.isEmpty());
     }
-    return computedDefaultLanguage;
+    return computedDefaultLanguage.toString();
 }
 
 String defaultLanguage()
 {
     Vector<String> languages = userPreferredLanguages();
     if (languages.size())
         return languages[0];
 
     return emptyString();
 }
@@ skipping 70 matching lines @@
     if (languageWithoutLocaleMatch.length())
         return languageWithoutLocaleMatchIndex;
 
     if (languageMatchButNotLocale.length())
         return languageMatchButNotLocaleMatchIndex;
 
     return languageList.size();
 }
 
 }