DO NOT MERGE Update libpng to 1.6.20 am: ed2e977a88 am: a2478bdf6e am: 7509e3018b am: 7fc8b69ecc  -s ours am: f4b20aeca4 am: fe9b944aeb
am: 2c5f8ed933  -s ours

* commit '2c5f8ed933d0e564d3684d5b7c56107a0140e335':

Change-Id: Ia6f247c695b8b9445c39342080d0c29f99c72494