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

Source/platform/Language.cpp

Index: Source/platform/Language.cpp
diff --git a/Source/platform/Language.cpp b/Source/platform/Language.cpp
old mode 100644
new mode 100755
index 535214cb0fc4cf58c91a849b77e384628a7971f2..f5c4f938e8af8098f71cbc69fd70609879977954
--- a/Source/platform/Language.cpp
+++ b/Source/platform/Language.cpp
@@ -27,18 +27,18 @@
 #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()