Roll 50: Copied IDLs, PYTHON scripts from WebKit removed deleted files in WebCore

core/streams/ReadableStreamReader.idl

 // 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.
 
 [
     GarbageCollected,
-    ActiveDOMObject,
+    DependentLifetime,
     Exposed=(Window,Worker),
     NoInterfaceObject,
 ] interface ReadableStreamReader {
     // FIXME: Add constructor.
 
     [CallWith=ScriptState] readonly attribute Promise<void> closed;
     [CallWith=ScriptState] Promise<any> read();
 
     [CallWith=ScriptState] Promise<void> cancel(optional any reason);
     [RaisesException] void releaseLock();
 };