Fix undefined shift in DiyFpStrtod.

This code is just copy pasta from v8, this patch copies a newer version
of the pasta.

https://chromium.googlesource.com/v8/v8/+/374a4da83e6f4e05d31640b23b5ca92f0bbf0586/src/strtod.cc#249

BUG=637044, 629034

Review-Url: https://chromiumcodereview.appspot.com/2438383003
Cr-Commit-Position: refs/heads/master@{#426973}

third_party/WebKit/Source/wtf/dtoa/strtod.cc

@@ -264,7 +264,7 @@ namespace double_conversion {
         const int kDenominator = 1 << kDenominatorLog;
         // Move the remaining decimals into the exponent.
         exponent += remaining_decimals;
-        int error = (remaining_decimals == 0 ? 0 : kDenominator / 2);
+        int64_t error = (remaining_decimals == 0 ? 0 : kDenominator / 2);
 
         int old_e = input.e();
         input.Normalize();