Camera 2: Add three metrics to cts performance test.

* Add single capture latency metric. Time is measured between
  sending out a request and getting the image data.
* Add partial result latency metric. Time is measured between
  sending out a request and getting the partial capture result.
* Add full result latency metric. Time is measured between
  sending out a request and getting the full capture result.

Change-Id: I6d3c18cdf25d976f3be389cdc244ba75953d9bf2