[Gutenberg] Integrate validator with Gutenberg blocks

[postphotos]

As a WordPress site running Gutenberg, my core blocks' AMP-HTML markup should be validated and results should appear in the Compatibility Tool.

• AC1: Integrate block validation results with the UI to reveal when a validation error does occur. Normally such errors will not happen for core blocks, but for the Custom HTML block in particular it is a distinct possibility. It is also key for plugins which introduce blocks so that their AMP validity can also be reported.

[westonruter]

See #902 (comment)

[westonruter]

I have some code for validation that is pending pushing.

[westonruter]

@kienstra See #1019. Next step is to communicate back the validation errors when saving a post in the Gutenberg editor, and then showing the validation error notice in the same way we're doing for the classic editor.

[postphotos]

The main issue description has been updated with a formal Story and Acceptance Criteria.

[kienstra]

Request For Testing

Hi @csossi,
Could you please test this when you can? It's not as important as the 0.7.1 regression testing, though.

1. Go to the editor of a post, like this. Your login details should be the same as the other testing sites.
2. Add a Custom HTML block
3. Enter invalid AMP, like:

<script>doSomething()</script>
<button onclick="doThis()">Click me</button>

4. Click "Save draft"
   Expected:

• A notice appears at the top of the editor, and at the top of the block
• The "Details" link in the top notice leads to a page that highlights where the error is

5. Add other blocks
   Expected:

• There aren't notices above those blocks, like there are above that Custom HTML block above
• The notice at the top of the page still appears

[csossi]

verified in QA