message: Make reasons and errors optional
diff: Exposed=(Window,Worker)]
  interface ReadableStream {
  readonly attribute boolean locked;
  - Promise<void> cancel(any reason);
  + Promise<void> cancel(optional any reason);
  ReadableStreamDefaultReader getReader();
  ReadableStreamBYOBReader getReader(any options);
  any pipeThrough(any pair, optional PipeOptions options);
  @@ -59,7 +59,7 @@ interface ReadableStreamReadResult {
  interface ReadableStreamDefaultReader {
  readonly attribute Promise<void> closed;
  - Promise<void> cancel(any reason);
  + Promise<void> cancel(optional any reason);
  Promise<ReadableStreamReadResult> read();
  void releaseLock();
  };
  @@ -69,7 +69,7 @@ interface ReadableStreamDefaultReader {
  interface ReadableStreamBYOBReader {
  readonly attribute Promise<void> closed;
  - Promise<void> cancel(any reason);
  + Promise<void> cancel(optional any reason);
  Promise<ReadableStreamReadResult> read(ArrayBufferView view);
  void releaseLock();
  };
  @@ -80,7 +80,7 @@ interface ReadableStreamDefaultController {
  void close();
  void enqueue(any chunk);
  - void error(any e);
  + void error(optional any e);
  };
  [Exposed=(Window,Worker)]
  @@ -90,7 +90,7 @@ interface ReadableByteStreamController {
  void close();
  void enqueue(ArrayBufferView chunk);
  - void error(any e);
  + void error(optional any e);
  };
  [Exposed=(Window,Worker)]
  @@ -105,7 +105,7 @@ interface ReadableStreamBYOBRequest {
  Exposed=(Window,Worker)]
  interface WritableStream {
  readonly attribute boolean locked;
  - Promise<void> abort(any reason);
  + Promise<void> abort(optional any reason);
  WritableStreamDefaultWriter getWriter();
  };
  @@ -127,7 +127,7 @@ interface WritableStreamDefaultWriter {
  readonly attribute unrestricted double? desiredSize;
  readonly attribute Promise<void> ready;
  - Promise<void> abort(any reason);
  + Promise<void> abort(optional any reason);
  Promise<void> close();
  void releaseLock();
  Promise<void> write(any chunk);
  @@ -135,7 +135,7 @@ interface WritableStreamDefaultWriter {
  [Exposed=(Window,Worker)]
  interface WritableStreamDefaultController {
  - void error(any e);
  + void error(optional any e);
  };
  [Constructor(optional Transformer transformer, optional QueuingStrategy writableStrategy, optional QueuingStrategy readableStrategy),
  @@ -157,7 +157,7 @@ interface TransformStreamDefaultController {
  readonly attribute unrestricted double? desiredSize;
  void enqueue(any chunk);
  - void error(any reason);
  + void error(optional any reason);
  void terminate();
  };
  