Reland of: chromeos: Add CPU temperature reader

Original issue: https://codereview.chromium.org/2823583002/

Reason for revert: Build errors due to non-exported symbols

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Reads from hwmon in sysfs.

This does the same thing as ReadCPUTempInfo() in
chrome/browser/chromeos/policy/device_status_collector.cc, but it is
available to the rest of Chrome.

BUG=chromium:709102

Review-Url: https://codereview.chromium.org/2838853002
Cr-Commit-Position: refs/heads/master@{#466999}
4 files changed