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

third_party/WebKit/Source/wtf/text/WTFString.h

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc.
  * All rights reserved.
  *
  * 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 86 matching lines @@
 
   // Construct a string referencing an existing StringImpl.
   String(StringImpl* impl) : m_impl(impl) {}
   String(PassRefPtr<StringImpl> impl) : m_impl(impl) {}
 
   void swap(String& o) { m_impl.swap(o.m_impl); }
 
   template <typename CharType>
   static String adopt(StringBuffer<CharType>& buffer) {
     if (!buffer.length())
-      return StringImpl::empty();
+      return StringImpl::empty;
     return String(buffer.release());
   }
 
   explicit operator bool() const { return !isNull(); }
   bool isNull() const { return !m_impl; }
   bool isEmpty() const { return !m_impl || !m_impl->length(); }
 
   StringImpl* impl() const { return m_impl.get(); }
   PassRefPtr<StringImpl> releaseImpl() { return m_impl.release(); }
 
@@ skipping 364 matching lines @@
 
 inline void swap(String& a, String& b) {
   a.swap(b);
 }
 
 // Definitions of string operations
 
 template <size_t inlineCapacity>
 String::String(const Vector<UChar, inlineCapacity>& vector)
     : m_impl(vector.size() ? StringImpl::create(vector.data(), vector.size())
-                           : StringImpl::empty()) {}
+                           : StringImpl::empty) {}
 
 template <>
 inline const LChar* String::getCharacters<LChar>() const {
   DCHECK(is8Bit());
   return characters8();
 }
 
 template <>
 inline const UChar* String::getCharacters<UChar>() const {
   DCHECK(!is8Bit());
@@ skipping 90 matching lines @@
 using WTF::String;
 using WTF::emptyString;
 using WTF::emptyString16Bit;
 using WTF::charactersAreAllASCII;
 using WTF::equal;
 using WTF::find;
 using WTF::isSpaceOrNewline;
 
 #include "wtf/text/AtomicString.h"
 #endif  // WTFString_h