DO NOT MERGE Update libpng to 1.6.20 am: 0b39f202aa  -s ours am: 9795c8684c am: d0107515e0 am: 7d9fa2ce0f  -s ours
am: fd386f8f05

* commit 'fd386f8f056cb3d6980a327be1007505227baf3d':
  DO NOT MERGE Update libpng to 1.6.20

Change-Id: I63a08da4727ef3c6556a2ec940a83be04e88c249