The first check in ByteLengthIsValid() says "nsTArray only handles
sizes up to INT32_MAX", but the actual requirement is that the
capacity is no larger than UINT32_MAX. The check is overly restrictive
if sizeof(E) is 1 byte, and overly permissive if sizeof(E) is greater
than 2 bytes. I removed this check. Internal nsTArray invariants
should be enforced by nsTArray methods.
The second check is trying to check for overflow, but that should just
be done using CheckedInt.
