Gallery2: Increase the size of the tiles when decoding images

BitmapRegionDecoder was refactored in Android N [1] and bigger tiles
are now better to render images, so increase the size of each tile.

[1] https://issuetracker.google.com/issues/37136991#comment11

BUGBASH-188
BUGBASH-299

Change-Id: Ie9c282fc5a98c9da6bb8ae3bcfe869b8b422a84b
1 file changed