Add WTF::String::emptyString16Bit

Source/wtf/text/WTFString.cpp

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007-2009 Torch Mobile, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 869 matching lines @@
     String result = String::createUninitialized(length, destination);
 
     copyLCharsFromUCharSource(destination, source, length);
 
     return result;
 }
 
 String String::make16BitFrom8BitSource(const LChar* source, size_t length)
 {
     if (!length)
-        return emptyString();
+        return emptyString(Force16BitEmpty);
 
     UChar* destination;
     String result = String::createUninitialized(length, destination);
 
     StringImpl::copyChars(destination, source, length);
 
     return result;
 }
 
 String String::fromUTF8(const LChar* stringStart, size_t length)
@@ skipping 318 matching lines @@
     // FIXME: This will return ok even when the string fits into a double but not a float.
     return static_cast<float>(toDoubleType<UChar, AllowTrailingJunk>(data, length, 0, parsedLength));
 }
 
 const String& emptyString()
 {
     DEFINE_STATIC_LOCAL(String, emptyString, (StringImpl::empty()));
     return emptyString;
 }
 
+const String& emptyString(Force16Bit)
+{
+    DEFINE_STATIC_LOCAL(String, emptyString, (StringImpl::empty(StringImpl::Force16BitEmpty)));
+    return emptyString;
+}
+
 } // namespace WTF
 
 #ifndef NDEBUG
 // For use in the debugger
 String* string(const char*);
 Vector<char> asciiDebug(StringImpl* impl);
 Vector<char> asciiDebug(String& string);
 
 void String::show() const
 {
@@ skipping 27 matching lines @@
     buffer.append('\0');
     return buffer;
 }
 
 Vector<char> asciiDebug(String& string)
 {
     return asciiDebug(string.impl());
 }
 
 #endif