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

Source/modules/fetch/Response.h

Index: Source/modules/fetch/Response.h
diff --git a/Source/modules/fetch/Response.h b/Source/modules/fetch/Response.h
index 018bcc0d4c2235ab766ab539443a9edde4058bd1..69768929bdbdf9fccfbde47802da4ea8e2735dec 100644
--- a/Source/modules/fetch/Response.h
+++ b/Source/modules/fetch/Response.h
@@ -57,15 +57,14 @@ public:
     // From Response.idl:
     Response* clone(ExceptionState&);
 
-    void populateWebServiceWorkerResponse(WebServiceWorkerResponse&);
+    // Does not call response.setBlobDataHandle().
+    void populateWebServiceWorkerResponse(WebServiceWorkerResponse& /* response */);
 
     bool hasBody() const;
 
-    PassRefPtr<BlobDataHandle> blobDataHandle() const override;
     BodyStreamBuffer* buffer() const override;
     String mimeType() const override;
 
-    PassRefPtr<BlobDataHandle> internalBlobDataHandle() const;
     BodyStreamBuffer* internalBuffer() const;
     String internalMIMEType() const;