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

Source/core/testing/ReadableStreamTestCase.h

+// 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.
+
+#ifndef ReadableStreamTestCase_h
+#define ReadableStreamTestCase_h
+
+#include "bindings/core/v8/ScriptState.h"
+#include "bindings/core/v8/ScriptWrappable.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class ReadableStreamTestRequest;
+class ReadableStreamTestSource;
+
+class ReadableStreamTestCase final : public GarbageCollected<ReadableStreamTestCase>, public ScriptWrappable {
+    DEFINE_WRAPPERTYPEINFO();
+
+public:
+    DECLARE_TRACE();
+
+    ReadableStreamTestCase(ScriptState*);
+
+    ReadableStreamTestRequest* request() { return m_request; }
+    ReadableStreamTestSource* source() { return m_source; }
+
+private:
+    Member<ReadableStreamTestSource> m_source;
+    Member<ReadableStreamTestRequest> m_request;
+};
+
+} // namespace blink
+
+#endif // ReadableStreamTestCase_h