Introduce ExclusiveStreamReader.

Source/core/streams/ExclusiveStreamReader.idl

-// Copyright 2014 The Chromium Authors. All rights reserved.
+// Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-enum ReadableStreamState {
-    "readable",
-    "waiting",
-    "closed",
-    "errored"
-};
-
 [
     RuntimeEnabled=ExperimentalStream,
     GarbageCollected,
+    ActiveDOMObject,
     Exposed=(Window,Worker),
-    ActiveDOMObject,
-] interface ReadableStream {
-    [CallWith=ScriptState, RaisesException] any read();
+] interface ExclusiveStreamReader {
+    // FIXME: Add constructor.
+
+    [CallWith=ScriptState] readonly attribute Promise closed;
+    readonly attribute boolean isActive;
     [CallWith=ScriptState] readonly attribute Promise ready;
-    [ImplementedAs=stateString] readonly attribute ReadableStreamState state;
+    // See ReadableStream.state.
+    readonly attribute DOMString state;
 
     [CallWith=ScriptState] Promise cancel(any reason);
-
-    [CallWith=ScriptState] readonly attribute Promise closed;
+    [CallWith=ScriptState, RaisesException] any read();
+    void releaseLock();
 };