[vm] Fix typo in calculation of native wrapper class size in precompiler configuration.
[vm] Fix typo in calculation of native wrapper class size in precompiler configuration.

At present there is difference in assembly output from SIMARM/gen_snapshot and SIMARM_X64/gen_snapshot around classes that extend native wrappers(for example, dart:io NativeSocket).

See dartbug.com/41824.

Change-Id: I944901ff4cccde972623c490d1d67d894fb03595
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/147808
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>
Commit-Queue: Alexander Aprelev <dfb74c35a357c2059971a4bf7fe26b6a7c18085d@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk