Reworking how pixel events on redirect to cart are handled.

[message-dimke]

This one came from Slack channel.

When using Stripe plugin from one of 3rd party devs there was an issue with Facebook pixel events duplicated since that extension was cloning cart to perform some calculations which resulted in triggering cart hooks on a cloned object doubling the events.

After the fix from above was merged in another thing happened. The code added to prevent events from firing on cloned carts was failing when redirect to cart after product added setting is on. The reason to that is the previous fix was operating cart item key which was not always present when the code was called outside woocomerce_add_to_cart hook.

Current PR reworks the mechanism how events are rendered on redirect to cart after product added to make things work w/o any issues.

Detailed test instructions:

1. Install Meta Pixel Helper Chrom extension. https://chromewebstore.google.com/detail/meta-pixel-helper/fdgfkebogiimcoedlicjlajpkdmockpc?pli=1
2. Install AJAX Add to cart button extension at will. https://wordpress.org/plugins/woo-ajax-add-to-cart/
3. Open WooCommerce Settings and check some boxes =)

4. Go to Shop page

5. Add some products into cart. In case of using AJAX extension page must not reload but Meta Pixel Helper must show Add to cart event. If w/o AJAX the page must reload and add the event.

6. Add some more products (multiple at once).

7. Observe Meta Pixel Helper chrome extension looking for AddToCart events.

8. Go to WooCommerce Settings again and update them as on the screen below.

9. Go back to the Shop page and Add something to the cart. The page must redirect to the cart page adding the product in and rendering the Pixel event.

10. And add some more. The page also must redirect to the cart page with Pixel events rendered.

11. When the cart page loads, observe the Meta Pixel Helper chrome extension. You must see a bunch of AddToCart events there.

Additional details:

Changelog entry

Fix - Facebook Pixel events missing on redirect to cart.

[budzanowski]

Thank you for the changes!