Currently, input invalidation for TTI is done on the browser side, while input invalidation for TTI is done on the renderer side. This leads to can lead to subtle bugs like  Issue 808536 . Once TTI definition is fully settled, we should unify the input invalidation story to prevent these in the future.

Additionally, if a TTI is invalidated by input today but the input happens before FMP, then FMP detector does not supply an FMP value and the TTI recording status is recorded as FMP not reached even though FMP was not reached because of an input event. Although technically this is working as intended, we should have a separate UMA to have better visibility into how often user input is the root cause of an aborted TTI.