Replace StringImpl::empty{16Bit}() with a static member

third_party/WebKit/Source/wtf/text/StringMac.mm

 /**
  * Copyright (C) 2006 Apple Computer, 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 12 matching lines @@
 #include <CoreFoundation/CFString.h>
 
 namespace WTF {
 
 String::String(NSString* str) {
   if (!str)
     return;
 
   CFIndex size = CFStringGetLength(reinterpret_cast<CFStringRef>(str));
   if (size == 0)
-    m_impl = StringImpl::empty();
+    m_impl = StringImpl::empty;
   else {
     Vector<LChar, 1024> lcharBuffer(size);
     CFIndex usedBufLen;
     CFIndex convertedsize =
         CFStringGetBytes(reinterpret_cast<CFStringRef>(str),
                          CFRangeMake(0, size), kCFStringEncodingISOLatin1, 0,
                          false, lcharBuffer.data(), size, &usedBufLen);
     if ((convertedsize == size) && (usedBufLen == size)) {
       m_impl = StringImpl::create(lcharBuffer.data(), size);
       return;
     }
 
     Vector<UChar, 1024> ucharBuffer(size);
     CFStringGetCharacters(reinterpret_cast<CFStringRef>(str),
                           CFRangeMake(0, size), ucharBuffer.data());
     m_impl = StringImpl::create(ucharBuffer.data(), size);
   }
 }
 
 }  // namespace WTF