Fix sky include guards to match Chromium style

sky/engine/core/animation/CompositorAnimationsImpl.h

Index: sky/engine/core/animation/CompositorAnimationsImpl.h
diff --git a/sky/engine/core/animation/CompositorAnimationsImpl.h b/sky/engine/core/animation/CompositorAnimationsImpl.h
index 4152c908f631e49b489c604a8df7f7e3e2b327d9..673a6507088a286af7237bf5410eab9501ab8f46 100644
--- a/sky/engine/core/animation/CompositorAnimationsImpl.h
+++ b/sky/engine/core/animation/CompositorAnimationsImpl.h
@@ -28,6 +28,9 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#ifndef SKY_ENGINE_CORE_ANIMATION_COMPOSITORANIMATIONSIMPL_H_
+#define SKY_ENGINE_CORE_ANIMATION_COMPOSITORANIMATIONSIMPL_H_
+
 #include "sky/engine/core/animation/AnimationEffect.h"
 #include "sky/engine/core/animation/KeyframeEffectModel.h"
 #include "sky/engine/core/animation/Timing.h"
@@ -59,3 +62,5 @@ private:
 };
 
 } // namespace blink
+
+#endif  // SKY_ENGINE_CORE_ANIMATION_COMPOSITORANIMATIONSIMPL_H_