chromeos: Add suspend result histograms.

Add Power.SuspendAttempt and Power.SuspendResult histograms.
Deprecate Power.SuspendStatus. Also make miscellaneous
corrections to descriptions of other Chrome OS histograms.

BUG=337520

Review URL: https://codereview.chromium.org/145083015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247388 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247388