Gallery2: fix timeline title become smaller after rotate screen.

onSlotSizeChanged() will be called after rotate screen, but all images and
timelint titles won't be updated if slot width has not changed,
so timeline title size become smaller.

Update timeline title in onSlotSizeChanged(),
make sure timeline title's size is correct.

Change-Id: I2064638f308bc11a019f6cb63678ce5e016a0c8f
CRs-Fixed: 966414