media summary: write to memo when no images found

[mreishus]

Proposed changes:

• Jetpack_Media_Summary::get() runs up to 4 times on a single post. It already has memoization, but it doesn't remember its results when it returns early. This adds the already-existing memoization to the early return path.
  • Originally added in Media Summary: improve performance with single page load caching #5938.

On my WPCOM sandbox this reduces the time spent in jetpack_og_tags() on a simple site with a few text posts from ~25ms to ~15ms (when viewing a single text post).

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• Create a simple post with no images
• Visit that post's page and view source
• The code between the <!-- Jetpack Open Graph Tags --> and <!-- End Jetpack Open Graph Tags --> should appear the same before and after the change
  • The callers are jetpack_open_graph_tags -> enhanced_og_image(), jetpack_open_graph_tags -> enhanced_og_video(), and jetpack_open_graph_tags -> enhanced_og_gallery()

./projects/plugins/jetpack/tests/php/media/test-class.jetpack-media-summary.php should also cover it (unsure how to run)

[github-actions]

Are you an Automattician? You can now test your Pull Request on WordPress.com. On your sandbox, run

bin/jetpack-downloader test jetpack update/media-summary-memo

to get started. More details: p9dueE-5Nn-p2

[github-actions]

Thank you for your PR!

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Jetpack plugin:

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[jeherve]

This seems to test well for me, I do not notice any changes in OG tags or Twitter cards on WordPress.com Simple or Jetpack when the Publicize module is active.

./projects/plugins/jetpack/tests/php/media/test-class.jetpack-media-summary.php should also cover it (unsure how to run)

It ran when you created the PR, but you can also run it locally by running jetpack docker -- --filter=WP_Test_Jetpack_MediaSummary