Fix sky include guards to match Chromium style

sky/engine/wtf/dtoa/bignum-dtoa.h

Index: sky/engine/wtf/dtoa/bignum-dtoa.h
diff --git a/sky/engine/wtf/dtoa/bignum-dtoa.h b/sky/engine/wtf/dtoa/bignum-dtoa.h
index 2e47790413320ef4174c4cb359ac470751a6190f..867b05dac9fe8c8cc15e1fd9632ae52483d5bc70 100644
--- a/sky/engine/wtf/dtoa/bignum-dtoa.h
+++ b/sky/engine/wtf/dtoa/bignum-dtoa.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_BIGNUM_DTOA_H_
-#define DOUBLE_CONVERSION_BIGNUM_DTOA_H_
+#ifndef SKY_ENGINE_WTF_DTOA_BIGNUM-DTOA_H_
+#define SKY_ENGINE_WTF_DTOA_BIGNUM-DTOA_H_
 
 #include "sky/engine/wtf/dtoa/utils.h"
 
@@ -83,4 +83,4 @@ namespace double_conversion {
 
 } // namespace WTF
 
-#endif  // DOUBLE_CONVERSION_BIGNUM_DTOA_H_
+#endif  // SKY_ENGINE_WTF_DTOA_BIGNUM-DTOA_H_