🐛amp-video-iframe: add additional iframe sandbox attributes allowing video-ad clickthrough

[klipstein]

Video ads (Pre-/Mid-/Postrolls) that get rendered inside amp-video-iframe currently cannot escape the given iframe sandbox. So that video-ad clickthrough targets can be opened by the embedded video-player the following iframe sandbox attributes were added:

• allow-popups-to-escape-sandbox
• allow-top-navigation-by-user-activation

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[klipstein]

I signed it!

[googlebot]

CLAs look good, thanks!

[alanorozco]

Thanks for this!

[klipstein]

@alanorozco do I need to adjust something in this pull so that it can be merged?

[alanorozco]

@klipstein Could you merge from the latest upstream master and push to this PR?

[klipstein]

@alanorozco I've merged latest master. Thanks for your help.

[alanorozco]

@klipstein Merged, thanks! Expect your changes to be in the next dev channel release.

[cramforce]

Oh hei @klipstein, good to see you on the internetz!

[klipstein]

@cramforce ohai! Glad to see you too and that you started this nice little project :)