GitLab

https://crrev.com/c/1539860 changed child throttling to allow only two
unembedded surfaces. However, this seems to have regressed latency so
revert back to allowing three unemedded surfaces.

Bug: 951992
Change-Id: I49f67d5299642063ef265aed34767f56f1706eb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1598419
Commit-Queue: Saman Sami <samans@chromium.org>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664461}