Standard gallery swipe: at fit scale a horizontal drag follows the
finger 1:1 (rubber-banded past the page edge); on release, past 25% of
the width or a fast flick (>0.35 px/ms), the neighbor in the list
opens with a 150 ms ease-out slide-in from the drag direction.
Short drags snap back; vertical drags at fit are inert; zoomed drags
still pan and pinch still zooms. Arrow keys navigate on desktop.
Verified on the emulator: left swipes advance, right swipe returns to
the previous image pixel-identical, 80px drag and vertical drag do not
navigate.
Greg Pomerantz
bca6a9de4a