Fix sky include guards to match Chromium style

sky/engine/wtf/dtoa/diy-fp.h

Index: sky/engine/wtf/dtoa/diy-fp.h
diff --git a/sky/engine/wtf/dtoa/diy-fp.h b/sky/engine/wtf/dtoa/diy-fp.h
index d1fdff2905b6f4d73bdb825d9e1e959d8a074e14..1a72ac6c57b7046b995e73589201e24d12fffd6c 100644
--- a/sky/engine/wtf/dtoa/diy-fp.h
+++ b/sky/engine/wtf/dtoa/diy-fp.h
@@ -25,8 +25,8 @@
 // (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 DOUBLE_CONVERSION_DIY_FP_H_
-#define DOUBLE_CONVERSION_DIY_FP_H_
+#ifndef SKY_ENGINE_WTF_DTOA_DIY-FP_H_
+#define SKY_ENGINE_WTF_DTOA_DIY-FP_H_
 
 #include "sky/engine/wtf/dtoa/utils.h"
 
@@ -119,4 +119,4 @@ namespace double_conversion {
 
 } // namespace WTF
 
-#endif  // DOUBLE_CONVERSION_DIY_FP_H_
+#endif  // SKY_ENGINE_WTF_DTOA_DIY-FP_H_