[automerger] libwebm: Cherrypick 5a41830 from upstream am: 0f99871368 am: 6b040ab5b6 am: 9a316baf5e am: 6cf161e924 am: 76f6b3b052
am: 76a6584c78

Change-Id: I782f782a16e86d69ed988eeb97f4f22e2b876e8c