Add tracking of process run time.

To help identify processes RAM growth over time, we keep
keep track of the total time the current process has been
running and its RAM use during that time.  Then we can look
at how large processes are based on how long they have been
running for.

See "Cur time" here:

  * com.google.android.inputmethod.latin / u0a124 / v26731214:
      Process com.google.android.inputmethod.latin:train (unique, 6 entries):
        SOff/Norm/(Cch Emty): +1m4s338ms
              Mod/(Cch Emty): +15s977ms
              Low/    Imp Bg: +6s272ms
                     Service: +239ms
                  (Cch Emty): +2s874ms
             Crit/    Imp Bg: +1s52ms
                       TOTAL: +1m30s752ms
        PSS/USS (1 entries):
          SOff/Norm/(Cch Emty): 11MB-11MB-11MB/5.6MB-5.7MB-5.7MB/5.6MB-34MB-62MB over 2
        Cur time +30s214ms: 11MB-11MB-11MB/5.7MB-5.7MB-5.7MB/62MB-62MB-62MB over 1
      Process com.google.android.inputmethod.latin (unique, 6 entries):
        SOff/Norm/    Imp Bg: +2h22m18s830ms
              Mod/    Imp Bg: +15s977ms
              Low/    Imp Bg: +12s98ms
             Crit/    Imp Bg: +32s815ms
         SOn/Norm/    Imp Bg: +53m13s63ms
             Crit/    Imp Bg: +4s170ms
                       TOTAL: +3h16m36s953ms
        PSS/USS (3 entries):
          SOff/Norm/    Imp Bg: 27MB-31MB-34MB/21MB-27MB-30MB/21MB-33MB-88MB over 11
                Mod/    Imp Bg: 25MB-29MB-32MB/19MB-23MB-26MB/19MB-56MB-92MB over 2
           SOn/Norm/    Imp Bg: 34MB-34MB-34MB/30MB-31MB-31MB/30MB-61MB-91MB over 2
        Cur time +2m47s741ms: 27MB-28MB-28MB/21MB-21MB-21MB/21MB-54MB-88MB over 2

Bug: 110957691
Test: manual
Change-Id: I33b291555fd125b3791752cb10de48300bb21706