During CL review of https://codereview.chromium.org/1856073002/, Andrei suggested that for unrecoverable errors (like IllegalArgumentExceptions), we should change mReadState and mWriteState to state.ERROR and notify clients through BidirectionalStream.Callback#onFailed, so clients clearly know that they cannot retry. If errors are recoverable, we should not throw IllegalArgumentException and allow clients to retry.

Assigning to myself right now. But feel free to do re-assign.