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Implement solution prototype for section expansion reflow issue
Closed, ResolvedPublicSpike

Description

Main idea to try first: deferring the expensive call to determine the location of lazy-loaded images until after the click event. This might still generate long tasks, but after the click. Which means it will stay out of First Input Delay.

The cost of the synchronous HTML rendering due to the section expansion will remain, and might still cause a slow event, but that part can only be resolved with something like Display Locking: T239295: Experiment with display locking for mobile sections

This task is only about removing the expensive viewport size calculations from the click event handler. Which should mitigate the slow event/slow first input delays.