GitLab

Just picked 10s arbitratily before we have a way to set this value via
Finch. Sending this out to see if collecting the average keyframe
distance and passing it via PipelineStatistics sounds reasonable.

BUG=663999
TEST=manual

Review-Url: https://codereview.chromium.org/2611333003
Cr-Commit-Position: refs/heads/master@{#443424}