Wrong LCP type captured in the DB

[jeawhanlee]

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• Using 3.16-pre-alpha
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Describe the bug
When a background image is identified as the LCP, the type in the DB reads img

To Reproduce
Steps to reproduce the behavior:

1. Use a background image as the LCP
2. Visit the page
3. See in DB that lcp type is captured as img

Expected behavior
We should capture background image LCP as bg-img instead of img

Screenshots
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Additional context
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Acceptance Criteria (for WP Media team use only)
Clear instructions for developers, to be added before the grooming

[MathieuLamiot]

Is this something that is not supposed to be covered by the existing issues?

[jeawhanlee]

@MathieuLamiot Yes I think it could be when modifying the beacon script because right now I see that the type is hardcoded here:

wp-rocket/inc/Engine/Media/AboveTheFold/AJAX/Controller.php

Line 58 in ca50f74

'type' => 'img',

But as of right now, I see that the beacon script captures the single background image.

[MathieuLamiot]

Ok, so let's fix this for single background images.