Change BodyStreamBuffer to be FetchDataConsumerHandle-based and enable backpressure in Fetch API

Source/modules/fetch/FetchManager.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/FetchManager.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/V8ThrowException.h"
 #include "core/dom/DOMArrayBuffer.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/fetch/FetchUtils.h"
 #include "core/fileapi/Blob.h"
 #include "core/frame/csp/ContentSecurityPolicy.h"
 #include "core/inspector/ConsoleMessage.h"
 #include "core/loader/ThreadableLoader.h"
 #include "core/loader/ThreadableLoaderClient.h"
 #include "modules/fetch/Body.h"
 #include "modules/fetch/BodyStreamBuffer.h"
+#include "modules/fetch/DataConsumerHandleUtil.h"
 #include "modules/fetch/FetchRequestData.h"
 #include "modules/fetch/Response.h"
 #include "modules/fetch/ResponseInit.h"
 #include "platform/network/ResourceError.h"
 #include "platform/network/ResourceRequest.h"
 #include "platform/network/ResourceResponse.h"
 #include "platform/weborigin/SecurityOrigin.h"
 #include "public/platform/WebURLRequest.h"
 #include "wtf/HashSet.h"
 
@@ skipping 72 matching lines @@
             break;
         case WebURLRequest::FetchRequestModeNoCORS:
             m_request->setResponseTainting(FetchRequestData::OpaqueTainting);
             break;
         case WebURLRequest::FetchRequestModeCORS:
         case WebURLRequest::FetchRequestModeCORSWithForcedPreflight:
             m_request->setResponseTainting(FetchRequestData::CORSTainting);
             break;
         }
     }
-    FetchResponseData* responseData = FetchResponseData::createWithBuffer(BodyStreamBuffer::create(handle, "Failed to fetch"));
+    FetchResponseData* responseData = FetchResponseData::createWithBuffer(BodyStreamBuffer2::create(createFetchDataConsumerHandleFromWebHandle(handle)));
     responseData->setStatus(response.httpStatusCode());
     responseData->setStatusMessage(response.httpStatusText());
     for (auto& it : response.httpHeaderFields())
         responseData->headerList()->append(it.key, it.value);
     responseData->setURL(response.url());
     responseData->setMIMEType(response.mimeType());
 
     FetchResponseData* taintedResponse = responseData;
     switch (m_request->tainting()) {
     case FetchRequestData::BasicTainting:
@@ skipping 323 matching lines @@
 
 DEFINE_TRACE(FetchManager)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_executionContext);
     visitor->trace(m_loaders);
 #endif
 }
 
 } // namespace blink