Enable srcset support in HTMLImageElement

Source/wtf/text/StringView.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 68 matching lines @@
     }
 
     const UChar* characters16() const
     {
         if (!m_impl)
             return 0;
         ASSERT(!is8Bit());
         return m_impl->characters16() + m_offset;
     }
 
+    PassRefPtr<StringImpl> toString() const
+    {
+        if (!m_impl)
+            return m_impl;
+        if (m_impl->is8Bit())
+            return StringImpl::create(characters8(), m_length);
+        return StringImpl::create(characters16(), m_length);
+    }
+
 private:
     RefPtr<StringImpl> m_impl;
     unsigned m_offset;
     unsigned m_length;
 };
 
 }
 
 using WTF::StringView;
 
 #endif