[automerger] Rework thumbnail cleanup am: 0dc23f95 skipped: 75767d1e am:...

[automerger] Rework thumbnail cleanup am: 0dc23f95 skipped: 75767d1e am: 6720ea0b am: 16ee12ac am: d08bb4b1 am: b3f50c9c  -s ours am: b50ae71d  -s ours am: 21e5aeef  -s ours am: ea89e699  -s ours
am: dc245c79  -s ours

Change-Id: I67af00920f8ffe033f3dc261cac8a20c13f4d77f