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

Change-Id: Ib8c87f793bee8c444cfae71e91511a56dfb2afac