[Fetch] Support various operations after reading data partially.

Source/modules/fetch/Response.cpp

 // Copyright 2014 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 "config.h"
 #include "modules/fetch/Response.h"
 
 #include "bindings/core/v8/Dictionary.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/dom/DOMArrayBuffer.h"
@@ skipping 283 matching lines @@
     // "The headers attribute's getter must return the associated Headers object."
     return m_headers;
 }
 
 Response* Response::clone(ExceptionState& exceptionState)
 {
     if (bodyUsed()) {
         exceptionState.throwTypeError("Response body is already used");
         return nullptr;
     }
-    // FIXME: We throw an error while cloning the Response which body was
-    // partially read. But in Request case, we don't. When the behavior of the
-    // partially read streams will be well defined in the spec, we have to
-    // implement the behavior correctly.
     if (streamAccessed()) {
-        bool dataLost = false;
-        BodyStreamBuffer* drainingStream = createDrainingStream(&dataLost);
-        if (dataLost) {
-            exceptionState.throwTypeError("Cloning the Response which body was partially read is not supported.");
-            return nullptr;
-        }
+        BodyStreamBuffer* drainingStream = createDrainingStream();
         m_response->replaceBodyStreamBuffer(drainingStream);
     }
     return Response::createClone(*this);
 }
 
 void Response::populateWebServiceWorkerResponse(WebServiceWorkerResponse& response)
 {
     m_response->populateWebServiceWorkerResponse(response);
 }
 
@@ skipping 57 matching lines @@
 }
 
 DEFINE_TRACE(Response)
 {
     Body::trace(visitor);
     visitor->trace(m_response);
     visitor->trace(m_headers);
 }
 
 } // namespace blink