Fix thumbnail disappearing during staged split animation

Previous set the thumbnail view to be visible initially. After deciding not to do so, forgot to put the visibility statement back. Also the transform matrix needs to reset before posting new scales.

Test: https://recall.googleplex.com/projects/f46cfe9c-8076-4efe-bf8a-b1cc4f1f5e1b/sessions/6576df3a-6d14-4b7e-8fb2-1c0a335472e4
Fixes: 194414938
Change-Id: I25fe39ea99943a3c1e2257681df3eb379bc30e51