integrate readablestream with fetch and blob

components/script/dom/webidls/Blob.webidl

@@ -17,6 +17,7 @@ interface Blob {
              optional [Clamp] long long end,
              optional DOMString contentType);
 
+  [NewObject] object stream();
   [NewObject] Promise<DOMString> text();
   [NewObject] Promise<ArrayBuffer> arrayBuffer();
 };

components/script/dom/webidls/Body.webidl

@@ -7,6 +7,7 @@
 [Exposed=(Window,Worker)]
 interface mixin Body {
   readonly attribute boolean bodyUsed;
+  readonly attribute object? body;
 
   [NewObject] Promise<ArrayBuffer> arrayBuffer();
   [NewObject] Promise<Blob> blob();

components/script/dom/webidls/ReadableStream.webidl

@@ -0,0 +1,11 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+// This interface is entirely internal to Servo, and should not be accessible to
+// web pages.
+
+[NoInterfaceObject, Exposed=(Window,Worker)]
+// Need to escape "ReadableStream" so it's treated as an identifier.
+interface _ReadableStream {
+};

components/script/dom/webidls/XMLHttpRequest.webidl

@@ -13,7 +13,7 @@
  */
 
 // https://fetch.spec.whatwg.org/#bodyinit
-typedef (Blob or BufferSource or FormData or DOMString or URLSearchParams) BodyInit;
+typedef (Blob or BufferSource or FormData or DOMString or URLSearchParams or ReadableStream) BodyInit;
 
 enum XMLHttpRequestResponseType {
   "",
@@ -21,7 +21,7 @@ enum XMLHttpRequestResponseType {
   "blob",
   "document",
   "json",
-  "text"
+  "text",
 };
 
 [Exposed=(Window,Worker)]