it's not that hard to measure latency. point a video camera at the screen and measure how long it takes from click to completion of new screen load.
then pick ten web pages and collect the data.
then pick ten other common UI actions (not in the web browser) and collect that data too. there's some fudge here because the phones have different UIs so you won't necessarily be able to find identical actions but you could get a good idea.
it's entirely possible that the dev teams have instrumented builds that give them this info automatically. i would be surprised if they didn't, in fact.
then pick ten web pages and collect the data.
then pick ten other common UI actions (not in the web browser) and collect that data too. there's some fudge here because the phones have different UIs so you won't necessarily be able to find identical actions but you could get a good idea.
it's entirely possible that the dev teams have instrumented builds that give them this info automatically. i would be surprised if they didn't, in fact.