Add dropped frame percent metric to video_PlaybackPerf

Currently video_PlaybackPerf has only dropped frame count metric. The
test plays a video for 30 seconds. The number of decoded and dropped
frames may vary in each run. Also, the dropped frame will change when
we change a test video. To have a more stable metric, add dropped
frame percent to video_PlaybackPerf.

BUG=chromium:510019
TEST=run the test on a veyron jerry

Change-Id: I729fd356feadbf6f0c142ddc22f046fe8250413a
Previous-Reviewed-on: https://chromium-review.googlesource.com/285369
(cherry picked from commit 4db6632e2476c6c480950ebb871553ab989421a4)
Reviewed-on: https://chromium-review.googlesource.com/288630
Reviewed-by: Wu-cheng Li <wuchengli@chromium.org>
Commit-Queue: Wu-cheng Li <wuchengli@chromium.org>
Tested-by: Wu-cheng Li <wuchengli@chromium.org>
1 file changed