Original commit message:
Make FieldType::None() non-nullptr value to avoid undefined behaviour
When FieldType::None() returns a cast Smi::FromInt(0), which translates
as nullptr, the FieldType::IsNone() check becomes equivalent to
`this == nullptr` which is not allowed by the standard and
therefore optimized away as a false constant by GCC 6.
This has lead to crashes when invoking methods on FieldType::None().
Using a different Smi constant for FieldType::None() makes the compiler
always include a comparison against that value. The choice of these
constants has no effect as they are effectively arbitrary.
BUG=https://github.com/nodejs/node/issues/8310
Review-Url: https://codereview.chromium.org/2292953002
Cr-Commit-Position: refs/heads/master@{#39023}
Fixes: https://github.com/nodejs/node/issues/8310
PR-URL: https://github.com/nodejs/node/pull/8411
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
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