Bug Description

When an iframe is set to be "full width" in the block editor, it is currently broken because its layout attribute defaults to 'intrinsic'.

Expected Behaviour

An iframe that is set to be "full width" in the block editor should have 'responsive' as its layout attribute.

Steps to reproduce

1. In the block editor, add an embed block and copy in the URL https://wordpress.tv/2019/10/08/the-history-of-wordpress-in-four-minutes/.
2. Set the alignment to "Full width".
3. Publish the post and visit it on its AMP URL.
4. The embedded video will not be full-width, but rather aligned to the left. Its markup shows that the it is set to layout=intrinsic.

Screenshots

Choosing the "Full width" alignment:

Comparison:

AMP markup:

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Acceptance criteria

• Iframe should look same in AMP as non-AMP

Implementation brief

• See Set layout to responsive if the iframe is aligned to full width #3507

QA testing instructions

• See instructions above.

Demo

• See screenshots.

Changelog entry

• Set iframe layout to responsive if the embed is aligned to full width.