Fix sky include guards to match Chromium style

sky/engine/core/html/canvas/MouseEventHitRegion.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef MouseEventHitRegion_h
-#define MouseEventHitRegion_h
+#ifndef SKY_ENGINE_CORE_HTML_CANVAS_MOUSEEVENTHITREGION_H_
+#define SKY_ENGINE_CORE_HTML_CANVAS_MOUSEEVENTHITREGION_H_
 
 #include "sky/engine/core/events/MouseEvent.h"
 #include "sky/engine/core/html/HTMLCanvasElement.h"
 #include "sky/engine/core/html/canvas/CanvasRenderingContext.h"
 #include "sky/engine/core/html/canvas/CanvasRenderingContext2D.h"
 
 namespace blink {
 
 class MouseEventHitRegion {
 public:
@@ skipping 16 matching lines @@
         String id = hitRegion->id();
         if (id.isEmpty())
             return String();
 
         return id;
     }
 };
 
 } // namespace blink
 
-#endif
+#endif  // SKY_ENGINE_CORE_HTML_CANVAS_MOUSEEVENTHITREGION_H_