DM: display current memory usage (instead of peak) when available.

Seems strictly more useful.

This implements Mac and Windows, which seemed easy.  Don't know how to do this on Linux yet.

BUG=skia:

CQ_EXTRA_TRYBOTS=client.skia:Test-Mac10.9-MacMini6.2-HD4000-x86_64-Debug-Trybot

NOTREECHECKS=true
TBR=halcanary@google.com

Review URL: https://codereview.chromium.org/990723002
4 files changed