[Backport] Reload cart totals when cart data changes

[tdgroot]

Original Pull Request

magento#18700

Reload cart totals when cart data changes

Description (*)

When cart data changes on cart view, the totals need to be reloaded. For example, when the qty changes, the totals of the cart data change as well.

This normally doesn't happen in default Magento, because cart mutations reload the entire page. I stumbled upon this problem when creating an extension that allows the customer to change qty without reloading the page.

Manual testing scenarios (*)

I can't really provide steps to reproduce my situation, because core Magento doesn't do javascript cart mutations on the cart view. But, when adding items to cart, the totals should be rendered properly. This change shouldn't affect the usual totals estimation. So here you go:

• Add an item to the cart.
• The totals should be initialized.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)