If a system instability is caused by some non-browser process, it will
be known from the total usage counters when crash dump is received.

Thus we can distinguish a case when some non-browser process is
misbehaving from other kinds of system resource exhaustion.

BUG=661461
R=thestig@chromium.org

Review-Url: https://codereview.chromium.org/2467283002
Cr-Commit-Position: refs/heads/master@{#430161}