WordAds: Update Head Loader

[dbspringer]

IPW provided a new faster/less intensive method to load the ad head scripts, this replaces the head.js load in insert_head_iponweb. While we're at it, let's update the dns-prefetch hints to use the WP builtin wp_resource_hints filter.

Changes proposed in this Pull Request:

• New faster, less intensive ad loading header script.
• Utilize wp_resource_hints filter for dns-prefetches.

Is this a new feature or does it add/remove features to an existing part of Jetpack?

• Update - p5UegX-qT-p2

Testing instructions:

1. Load patch on Jetpack site with active WordAds module.
2. Verify ads are still loading and dns-prefetch hints are in source.

Proposed changelog entry for your changes:

• Improved speed & resource use of Ads loading scripts.

[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 cad313a

[jeherve]

This looks good to me but I don't have any ads on my sites so I can't test all of it. I'll let someone else jump in. @kraftbj maybe, I think you have an active WordAds site?

[kraftbj]

Misfired on the mouse.

A couple of issues that I don't think are related to the PR, just things the ad networks are doing:

The script from “https://secure.adnxs.com/bounce?%2Fasync_usersync%3Fcbfn%3DAN_async_load” was loaded even though its MIME type (“text/html”) is not a valid JavaScript MIME type. async_usersync.html

Loading mixed (insecure) display content “http://sync.go.sonobi.com/us.gif?nw=en&nuid=bdd883ce-ccca-4bcb-afe0-74f8c4570870” on a secure page

[dbspringer]

A couple of issues that I don't think are related to the PR, just things the ad networks are doing:

Yeah, it's possible one of the ad creatives is using junky calls, it happens way too often 😐 That should be unrelated to our side of the equation though.