Fix sky include guards to match Chromium style

sky/engine/wtf/dtoa/cached-powers.h

Index: sky/engine/wtf/dtoa/cached-powers.h
diff --git a/sky/engine/wtf/dtoa/cached-powers.h b/sky/engine/wtf/dtoa/cached-powers.h
index 987cb3d5d0389511021628fb743419360eeb057b..36ec9e3a4e6403fa8b297fabdfe76327c6c3f616 100644
--- a/sky/engine/wtf/dtoa/cached-powers.h
+++ b/sky/engine/wtf/dtoa/cached-powers.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_CACHED_POWERS_H_
-#define DOUBLE_CONVERSION_CACHED_POWERS_H_
+#ifndef SKY_ENGINE_WTF_DTOA_CACHED-POWERS_H_
+#define SKY_ENGINE_WTF_DTOA_CACHED-POWERS_H_
 
 #include "diy-fp.h"
 
@@ -64,4 +64,4 @@ namespace double_conversion {
 
 } // namespace WTF
 
-#endif  // DOUBLE_CONVERSION_CACHED_POWERS_H_
+#endif  // SKY_ENGINE_WTF_DTOA_CACHED-POWERS_H_