struct MinSize

Vector traits:

MinSize is 0 (i.e., admit empty vector); take MinSize

<T

>()-byte chunks from

|src| for constructing instances of T. Allocating larger-than-min-size

T-instances is currently unsupported.

Caveat: When MinSize

<T

>() = 0, treat T-instances as though they will

allocate 8 bytes, enough for a 64-bit pointer.

TODO(https://fxbug.dev/42099318): Consume some input bytes to allocate pseudorandom number of items.