Fix sky include guards to match Chromium style

sky/engine/public/platform/WebExternalTextureMailbox.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 10 matching lines @@
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef WebExternalTextureMailbox_h
-#define WebExternalTextureMailbox_h
+#ifndef SKY_ENGINE_PUBLIC_PLATFORM_WEBEXTERNALTEXTUREMAILBOX_H_
+#define SKY_ENGINE_PUBLIC_PLATFORM_WEBEXTERNALTEXTUREMAILBOX_H_
 
 namespace blink {
 
 struct WebExternalTextureMailbox {
     signed char name[64];
     unsigned syncPoint;
     bool allowOverlay;
 
     WebExternalTextureMailbox()
         : syncPoint(0)
         , allowOverlay(false)
     {
         memset(name, 0, sizeof(name));
     }
 };
 
 inline bool nameEquals(const WebExternalTextureMailbox& a, const WebExternalTextureMailbox& b)
 {
     return !memcmp(a.name, b.name, sizeof(a.name));
 }
 
 } // namespace blink
 
-#endif // WebExternalTextureMailbox_h
+#endif  // SKY_ENGINE_PUBLIC_PLATFORM_WEBEXTERNALTEXTUREMAILBOX_H_