// We play this game because we want this to be callable even from places that
    // don't have access to CallFrame* or the VM, and we only allocate so little
    // memory here that it's not necessary to trigger a GC - just accounting what
    // we have done is good enough. The sort of bizarre exception to the "allocating
    // little memory" is when we transfer a backing buffer into the C heap; this
    // will temporarily get counted towards heap footprint (incorrectly, in the case
    // of adopting an oversize typed array) but we don't GC here anyway. That's
    // almost certainly fine. The worst case is if you created a ton of fast typed
    // arrays, and did nothing but caused all of them to slow down and waste memory.
    // In that case, your memory footprint will double before the GC realizes what's
    // up. But if you do *anything* to trigger a GC watermark check, it will know
    // that you *had* done those allocations and it will GC appropriately.