[Video] Record the results of background video optimization checks.

[Video] Record the results of background video optimization checks.

Each time we check whether to pause or disable video for backgrounded
media elements, record the result along with the reason.

BUG=None
TEST=manual

[whywhat, 2017-04-14 00:09:43]

avayvod@chromium.org changed reviewers:
+ dalecurtis@chromium.org

[whywhat, 2017-04-14 00:09:44]

PTaL

Some caveats:
- we will record something anytime when IsBackgroundOptimizationCandidate is
called, even if without an intent to optimize the video
- the intent is mostly figured out by whether the video has audio or not

I guess I should instead pass a callback to IsBackgroundOptimizationCandidate
when calling it (so it can be either null or RecordShouldPauseWhenHiddenResult
or RecordShouldDisableVideoWhenHiddenResult).

This won't solve the problem of recording this many times per video if it's
being backgrounded, with a different result because of the keyframe distance. I
could ignore the result if the distance is not calculated yet (0) and remember
if it's recorded so only record it once.

Sending this early to get initial feedback on my thoughts above :)

[DaleCurtis, 2017-04-14 01:21:55]

Hmm, what are we trying to solve here? Or are you just trying to figure out the
number of times we'd actually try to optimize? code-wise lgtm, but not sure what
we'll get out of it.