Fix sky include guards to match Chromium style

sky/engine/wtf/text/StringImpl.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
-#ifndef StringImpl_h
-#define StringImpl_h
+#ifndef SKY_ENGINE_WTF_TEXT_STRINGIMPL_H_
+#define SKY_ENGINE_WTF_TEXT_STRINGIMPL_H_
 
 #include <limits.h>
 #include "sky/engine/wtf/ASCIICType.h"
 #include "sky/engine/wtf/Forward.h"
 #include "sky/engine/wtf/HashMap.h"
 #include "sky/engine/wtf/StringHasher.h"
 #include "sky/engine/wtf/Vector.h"
 #include "sky/engine/wtf/WTFExport.h"
 #include "sky/engine/wtf/unicode/Unicode.h"
 
@@ skipping 679 matching lines @@
 
 }
 
 using WTF::StringImpl;
 using WTF::equal;
 using WTF::equalNonNull;
 using WTF::TextCaseSensitivity;
 using WTF::TextCaseSensitive;
 using WTF::TextCaseInsensitive;
 
-#endif
+#endif  // SKY_ENGINE_WTF_TEXT_STRINGIMPL_H_