Make sure we didn't regress performance / smoothness with new tile loading logic

I'm still worried that the new way to load tiles (after #2382) can affect performance considerably in some cases, although there was no other way to be able implement `flyTo`. We need to find a way to measure the map browsing experience compared to the old way, and optimize if necessary. cc @jfirebaugh 

Also known glitch to fix: #3053
