Fix sky include guards to match Chromium style

sky/engine/public/platform/WebCanvas.h

Index: sky/engine/public/platform/WebCanvas.h
diff --git a/sky/engine/public/platform/WebCanvas.h b/sky/engine/public/platform/WebCanvas.h
index eecd4644c1cc4ff1faf822037cf119bab0c3fd6c..759697422c5db5709e8b94e853ac7086b3e17984 100644
--- a/sky/engine/public/platform/WebCanvas.h
+++ b/sky/engine/public/platform/WebCanvas.h
@@ -28,8 +28,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef WebCanvas_h
-#define WebCanvas_h
+#ifndef SKY_ENGINE_PUBLIC_PLATFORM_WEBCANVAS_H_
+#define SKY_ENGINE_PUBLIC_PLATFORM_WEBCANVAS_H_
 
 #include "sky/engine/public/platform/WebCommon.h"
 
@@ -41,4 +41,4 @@ typedef SkCanvas WebCanvas;
 
 } // namespace blink
 
-#endif
+#endif  // SKY_ENGINE_PUBLIC_PLATFORM_WEBCANVAS_H_