CRAS: server_metrics - Log number of missed callback schedules

We record two UMA logs to check what is the frequency that the audio
thread misses callback schedules.

1. MissingCallbackFrequencyInput/Output
The number of missed callbacks for a day. It is calculated by
number of the missed callbacks / runtime of the stream.

2. MissingCallbackFirstTimeInput/Output
When the first time audio thread misses callback schedule, record how
many seconds have passed since stream started running.

BUG=chromium:918462
TEST=These UMA logs can be recorded well on peppy.

Change-Id: I588e59870d6668f3828bca0255d7703e4a42187a
Reviewed-on: https://chromium-review.googlesource.com/1392966
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
12 files changed