[WebComponent] Avoid layout/reflow where possible

Read into layout/reflow. Avoid inefficient operations where possible. Starting resources [here](https://gist.github.com/paulirish/5d52fb081b3570c81e3a), [here](https://developers.google.com/speed/docs/insights/browser-reflow), [here](https://developer.mozilla.org/en-US/Firefox/Performance_best_practices_for_Firefox_fe_engineers) and [here](https://3perf.com/talks/web-perf-101/).

Start by reading the four linked layout and reflow resources, then locate the WebComponent implementation in the repository. No file, test, or specific operation is identified in the issue, so the affected entry point and measurable definition of done must be established before work begins.

Written by the indexing model from the issue text.