Add methods for creating V8 extras-based ReadableStreams from C++

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 10 matching lines @@
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
     DoNotCheckConstants,
     GarbageCollected,
     TypeChecking=Interface,
+    ConstructorCallWith=ScriptState,
 ] interface Internals {
     DOMString address(Node node);
 
     GCObservation observeGC(any observed);
 
     [RaisesException, TypeChecking=Interface] DOMString elementLayoutTreeAsText(Element element);
     boolean isPreloaded(DOMString url);
     boolean isLoadingFromMemoryCache(DOMString url);
 
     [TypeChecking=Interface] boolean isSharingStyle(Element element1, Element element2);
@@ skipping 271 matching lines @@
     void setVisualViewportOffset(long x, long y);
 
     boolean isUseCounted(Document document, long useCounterId);
 
     iterable<long>;
 
     [Unscopeable] readonly attribute DOMString unscopeableAttribute;
     [Unscopeable] DOMString unscopeableMethod();
 
     ClientRectList focusRingRects(Element element);
+
+    readonly attribute any readableStream;
 };