Always pause background video-only media on desktop too.

Android has had this behavior for some time now. As of M62 we've
launched background optimizations for MSE, we can also enable
background pause support for video-only clips for src=.

BUG=663999,703411
TEST=experiment data looks good; ~98% of resume < 1s.

Change-Id: I8a2435579c7c996702c08f22ea398abc28e46cdf
Reviewed-on: https://chromium-review.googlesource.com/651237
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500749}
2 files changed