Cleanup time_format.cc, mostly cosmetic, one minor fix

This is a follow-up to the TimeRemainingShort() --> TimeDurationShort()
rename.  It renames some internal variables to match the new publicly
visible function name and consistently orders all occurrences of the
different time formats.  That way, a missing case in one of the switch
statements was found and corrected.

BUG=none

Review URL: https://codereview.chromium.org/155843003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249401 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249401
Fix import error in mac_platform_backend.py

The import of telemetry.core.util was hiding ctype.util. Fix this
by using ctype.util explicitly

TBR=tonyg@chromium.org
NOTRY=true
BUG=341446

Review URL: https://codereview.chromium.org/144463006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249402 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249402