Photon Functions: PHPCS fixes

[kraftbj]

functions.photon.php contains a number of PHPCS issues and use of outdated methods (parse_url with a wrapper to incompletely do what wp_parse_url does now, seeding a rand, etc).

The major change is to the way we determine the subdomain. The issue with the previous way, beyond the PHPCS violation, is that srand is disabled on some systems. The benefit of seeding with the image URL is to net a consistent subdomain to avoid the same image being served from two different subdomains, thus having a browser download the same image twice.

Since we don't really need anything particular randomized, we can convert the image path to a value between 0 and 2 using a combo of abs, crc32 and the % operator.

Changes proposed in this Pull Request:

• PHPCS fix and modernize Photon functions.

Testing instructions:

• WIth Jetpack and Image CDN/Photon, verify Photon URL is the same as before.

Proposed changelog entry for your changes:

• n/a, part of a general line item wrt PHPCS repair.

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: November 5, 2019.
Scheduled code freeze: October 29, 2019

Generated by 🚫 dangerJS against 4f59b6c

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello kraftbj! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D27441-code before merging this PR. Thank you!

[kraftbj]

Moving this out of milestone so I can look at the wp.com diff in more detail before merging here.

[stale]

This PR has been marked as stale. This happened because:

• It has been inactive in the past 3 months.
• It hasn’t been labeled `[Pri] Blocker`, `[Pri] High`.

No further action is needed. But it's worth checking if this PR has clear testing instructions, is it up to date with master, and it is still valid. Feel free to close this issue if you think it's not valid anymore — if you do, please add a brief explanation.

[matticbot]

kraftbj, Your synced wpcom patch D27441-code has been updated.

[kraftbj]

Fusion trips up a bit when there are changes at the beginning of a file (e.g. new file-level docblock) when the corresponding wpcom file has the "this is in Jetpack" notice. Manually patched in D27441-code.

[matticbot]

kraftbj, Your synced wpcom patch D27441-code has been updated.

[kraftbj]

The only functional change is the subdomain determination. Per the advice of Systems ( pMz3w-arH-p2 ), in 7.9, I'd like to only use the new technique for 1/3rd of URLs and then roll out to another third in 8.0, etc.