CV: Add content attribute handling + test
This patch adds a content attribute parsing and a wpt test for
contentvisibilityautostatechange event
Change-Id: Iae610a794477d3ca0b346b752b489cd101399fcc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5570779
Commit-Queue: Vladimir Levin vmpstr@chromium.org
Reviewed-by: Khushal Sagar khushalsagar@chromium.org
Cr-Commit-Position: refs/heads/main@{#1305905}