Use ldexp instead of pow for more accuracy.

src/conversions-inl.h

Index: src/conversions-inl.h
diff --git a/src/conversions-inl.h b/src/conversions-inl.h
index b098a1c29c1022e1c03057a58e319e5740af0e50..77b260f036483962892a88ec04f46624fca30aec 100644
--- a/src/conversions-inl.h
+++ b/src/conversions-inl.h
@@ -228,9 +228,7 @@ double InternalStringToIntDouble(UnicodeCache* unicode_cache,
   }
 
   ASSERT(number != 0);
-  // The double could be constructed faster from number (mantissa), exponent
-  // and sign. Assuming it's a rare case more simple code is used.
-  return static_cast<double>(negative ? -number : number) * pow(2.0, exponent);
+  return ldexp(static_cast<double>(negative ? -number : number), exponent);
 }