blink: Optimize check for vt participants.

R=vmpstr@chromium.org

Change-Id: Id66d14ee73f9bbb18f912694897deb843147b512
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5530186
Auto-Submit: Khushal Sagar <khushalsagar@chromium.org>
Commit-Queue: Khushal Sagar <khushalsagar@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: Vladimir Levin <vmpstr@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1300031}