Memory size: better alignment of dart memory tools with native memory tools

Numbers in DevTools > Memory should match numbers in native tools.

Different tools show different total memory consumption numbers, not apple to apple or not sync or not precise: mac usage monitor, DevTools > Memory > diff (total heap, reachable heap), DevTools > Memory > profile, DevTools > Memory > chart, in-process ProcessInfo.rss.

Start in DevTools > Memory and compare the diff, profile, and chart values with macOS Activity Monitor and in-process ProcessInfo.rss. The issue does not name files, tests, or a precise expected relationship between measurements. Done would require an agreed definition of total memory and aligned values across the listed tools.

Written by the indexing model from the issue text.