updated streams ponyfill

app/streams.js

@@ -0,0 +1,35 @@
+/* global TransformStream ReadableStream */
+import { createReadableStreamWrapper } from '@mattiasbuelens/web-streams-adapter';
+import {
+  TransformStream as TransformStreamPony,
+  ReadableStream as ReadableStreamPony
+} from 'web-streams-ponyfill';
+
+const toNativeReadable = createReadableStreamWrapper(ReadableStream);
+const toPonyReadable = createReadableStreamWrapper(ReadableStreamPony);
+
+export let TStream;
+if (typeof TransformStream === 'function') {
+  TStream = TransformStream;
+} else {
+  TStream = TransformStreamPony;
+  TStream.prototype.isPony = true;
+}
+
+export let RStream = ReadableStream;
+try {
+  new ReadableStream().pipeThrough(new TransformStream());
+} catch (e) {
+  RStream = ReadableStreamPony;
+  RStream.prototype.isPony = true;
+  RStream.prototype.toNative = function() {
+    return toNativeReadable(this);
+  };
+}
+
+export function wrapReadable(stream) {
+  if (RStream === ReadableStream) {
+    return stream;
+  }
+  return toPonyReadable(stream);
+}