Test page on iframe update.

src1: https://csreis.github.io

src2: https://build.chromium.org

src3: ../fixed-pos.html

Embedded Youtube video: https://www.youtube.com/embed/5SEV_g6gKCw

Same-domain video src1: ../../15-html5-video/player.html

Same-domain video src2: ../../63-video/video_captions.html