Fix sky include guards to match Chromium style

sky/engine/wtf/PageAllocator.h

Index: sky/engine/wtf/PageAllocator.h
diff --git a/sky/engine/wtf/PageAllocator.h b/sky/engine/wtf/PageAllocator.h
index b99a5f01ca3f628b029adf9604a80f42629336d3..de0d2665c1611f2f1f08f8913e7a46a7de3f6c80 100644
--- a/sky/engine/wtf/PageAllocator.h
+++ b/sky/engine/wtf/PageAllocator.h
@@ -28,8 +28,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef WTF_PageAllocator_h
-#define WTF_PageAllocator_h
+#ifndef SKY_ENGINE_WTF_PAGEALLOCATOR_H_
+#define SKY_ENGINE_WTF_PAGEALLOCATOR_H_
 
 #include <stdint.h>
 #include "sky/engine/wtf/Assertions.h"
@@ -99,4 +99,4 @@ WTF_EXPORT void recommitSystemPages(void* addr, size_t len);
 
 } // namespace WTF
 
-#endif // WTF_PageAllocator_h
+#endif  // SKY_ENGINE_WTF_PAGEALLOCATOR_H_