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The CL adds UMA for the number of seconds:

 * between HardUnplugged event and Suspend event
 * between SuspendDone event and HardUnplugged event

The numbers are needed for setting the best suppresing time for the hard
unplugged event.

BUG=433734
TEST=None

Review URL: https://codereview.chromium.org/723923004

Cr-Commit-Position: refs/heads/master@{#306523}