fix missing import.
Handle multi-line counters.

* treat the rate line as a COUNTER instead of UNKNOWN
* adjust counts in tests.
* Stat.name described to apply to multiline metrics only (counters and timers)
* StatCollection treats counters special like timers.
* Update the stat line parsers to recognize rate and count lines.
* Remove COUNTER from the list of simple types.
* Modify the tests to check for null values in the stats and metrics (they shouldn't be allowed).