This CL adds new fuzzer tests for the DecodeRedundant and IncomingPacket methods of AudioDecoder. In practice, only Opus has DecodeRedundant, and only iSAC has IncomingPacket. Did some minor work to generalize the helper function reading values from the fuzzed input. BUG=webrtc:5306 R=pbos@webrtc.org NOTRY=true Review URL: https://codereview.webrtc.org/1607173003 Cr-Commit-Position: refs/heads/master@{#11533}