Both PrivateMemoryFootprint and SharedMemoryFootprint should be additive. As such, we can compute a Memory Footprint for each process [Private + Shared], and a Memory Footprint for all chrome processes.

As a sanity check, this number should be reasonably close to the number of physical pages free when there is no swapped/compressed memory, and discounting mapped files.

On macOS, the current calculation for PMF overcounts by anonymous, paged-in shared memory. We should now be able to compute this, and subtract it out from the total.