Lazy loading of iframe gadgets on dashboard is broken

Issue Summary

This is reproducible on Data Center: yes

Steps to Reproduce

1. Have multiple gadgets on dashboard. At least one iframe gadget should be initially positioned outside the viewport.
2. Check the network tab to observe the calls happening to get the iframe content.

Expected Results

The content of iframe gadget should be loaded only when the gadget is within the viewport.

Actual Results

The content of all iframe gadgets is loaded on page load, regardless of their position on a page.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available