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On ChromeOS, kernel notifies Chrome when system gets into low memory
condition. However the low memory calculation misses a parameter
|min_free_kbytes| so the notification comes too late. A kernel fix is
coming to fix the issue.

On Chrome side, TabManager tries to recover memory to normal level. It
mirrors the low memory calculation in kernel to know how many tabs to
kill. So the missing parameter |min_free_kbytes| should be added back.

In the future, try to consolidate the logic in kernel so TabManager
doesn't need to do its own calculation.

BUG=chromium:645512,chrome-os-partner:60498
TEST=cave,peppy,etc.

Review-Url: https://codereview.chromium.org/2618483002
Cr-Commit-Position: refs/heads/master@{#442018}