Fix sky include guards to match Chromium style

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

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-#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"
 
 namespace WTF {
 
 namespace double_conversion {
 
     enum BignumDtoaMode {
         // Return the shortest correct representation.
         // For example the output of 0.299999999999999988897 is (the less accurate but
@@ skipping 36 matching lines @@
     //   Halfway cases are again rounded up.
     // 'BignumDtoa' expects the given buffer to be big enough to hold all digits
     // and a terminating null-character.
     void BignumDtoa(double v, BignumDtoaMode mode, int requested_digits,
                     Vector<char> buffer, int* length, int* point);
 
 }  // namespace double_conversion
 
 } // namespace WTF
 
-#endif  // DOUBLE_CONVERSION_BIGNUM_DTOA_H_
+#endif  // SKY_ENGINE_WTF_DTOA_BIGNUM-DTOA_H_