Always use at least 2 frame threads with dav1d.

Shows significant performance regression on even low core CrOS devices
otherwise on the following test case:
http://crosvideo2.appspot.com/?codec=av1&resolution=720

ARM 4 cores: 3%->17% dropped frame increase.
Intel Skylake 2 cores: 0.5% -> 3% dropped frame increase.

BUG=954659,957511
TEST=none
TBR=hiroh

Change-Id: I3073ca88548e9183dda5ce4d451c5c802a592213
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1602852
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658233}
1 file changed