Make Response::body return v8-extra based stream behind flag

third_party/WebKit/Source/core/streams/UnderlyingSourceBase.cpp

 // Copyright 2016 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.
 
 #include "core/streams/UnderlyingSourceBase.h"
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/ScriptValue.h"
 #include "core/streams/ReadableStreamController.h"
@@ skipping 49 matching lines @@
 {
     // This will return false within a finite time period _assuming_ that
     // consumers use the controller to close or error the stream.
     // Browser-created readable streams should always close or error within a
     // finite time period, due to timeouts etc.
     return m_controller && m_controller->isActive() && m_isStreamLocked;
 }
 
 void UnderlyingSourceBase::stop()
 {
-    m_controller->noteHasBeenCanceled();
-    m_controller.clear();
+    if (m_controller) {
+        m_controller->noteHasBeenCanceled();
+        m_controller.clear();
+    }
 }
 
 DEFINE_TRACE(UnderlyingSourceBase)
 {
     ActiveDOMObject::trace(visitor);
     visitor->trace(m_controller);
 }
 
 } // namespace blink