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

Source/modules/serviceworkers/RespondWithObserver.cpp

Index: Source/modules/serviceworkers/RespondWithObserver.cpp
diff --git a/Source/modules/serviceworkers/RespondWithObserver.cpp b/Source/modules/serviceworkers/RespondWithObserver.cpp
index 0754ab86355f0a26cfea1338eca57127e8c427ba..3cd14dc7775376b5c643c05792ff55344fa2a86b 100644
--- a/Source/modules/serviceworkers/RespondWithObserver.cpp
+++ b/Source/modules/serviceworkers/RespondWithObserver.cpp
@@ -10,6 +10,7 @@
 #include "bindings/core/v8/ScriptValue.h"
 #include "bindings/core/v8/V8Binding.h"
 #include "bindings/modules/v8/V8Response.h"
+#include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/inspector/ConsoleMessage.h"
 #include "core/streams/Stream.h"
@@ -204,15 +205,21 @@ void RespondWithObserver::responseWasFulfilled(const ScriptValue& value)
         return;
     }
     response->lockBody(Body::PassBody);
-    if (BodyStreamBuffer* buffer = response->internalBuffer()) {
+    if (BodyStreamBuffer2* buffer = response->internalBuffer()) {
         if (buffer == response->buffer() && response->isBodyConsumed())
             buffer = response->createDrainingStream();
         WebServiceWorkerResponse webResponse;
         response->populateWebServiceWorkerResponse(webResponse);
+        if (RefPtr<BlobDataHandle> blobDataHandle = buffer->handle()->obtainReader(nullptr)->drainAsBlobDataHandle()) {
+            webResponse.setBlobDataHandle(blobDataHandle);
+            ServiceWorkerGlobalScopeClient::from(executionContext())->didHandleFetchEvent(m_eventID, webResponse);
+            m_state = Done;
+            return;
+        }
         Stream* outStream = Stream::create(executionContext(), "");
         webResponse.setStreamURL(outStream->url());
         ServiceWorkerGlobalScopeClient::from(executionContext())->didHandleFetchEvent(m_eventID, webResponse);
-        StreamUploader* uploader = new StreamUploader(buffer, outStream);
+        StreamUploader* uploader = new StreamUploader(BodyStreamBuffer::create(buffer->releaseHandle(), "Failed"), outStream);
         uploader->start();
         m_state = Done;
         return;