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

Source/modules/fetch/FetchRequestData.h

Index: Source/modules/fetch/FetchRequestData.h
diff --git a/Source/modules/fetch/FetchRequestData.h b/Source/modules/fetch/FetchRequestData.h
index 788ba4fd4efaaa8fb266e657e36264e2fa98fc49..6ae5e9dae9952769014398ddaf847798c1ba5610 100644
--- a/Source/modules/fetch/FetchRequestData.h
+++ b/Source/modules/fetch/FetchRequestData.h
@@ -18,6 +18,8 @@
 namespace blink {
 
 class BlobDataHandle;
+class BodyStreamBuffer2;
+class ExecutionContext;
 class FetchHeaderList;
 class SecurityOrigin;
 class WebServiceWorkerRequest;
@@ -56,9 +58,9 @@ public:
     };
 
     static FetchRequestData* create();
-    static FetchRequestData* create(const WebServiceWorkerRequest&);
-    FetchRequestData* clone() const;
-    FetchRequestData* pass() const;
+    static FetchRequestData* create(ExecutionContext*, const WebServiceWorkerRequest&);
+    FetchRequestData* clone(ExecutionContext*) const;
+    FetchRequestData* pass(ExecutionContext*) const;
     ~FetchRequestData();
 
     void setMethod(AtomicString method) { m_method = method; }
@@ -84,7 +86,8 @@ public:
     FetchHeaderList* headerList() const { return m_headerList.get(); }
     void setHeaderList(FetchHeaderList* headerList) { m_headerList = headerList; }
     PassRefPtr<BlobDataHandle> blobDataHandle() const { return m_blobDataHandle; }
-    void setBlobDataHandle(PassRefPtr<BlobDataHandle> blobHandle) { m_blobDataHandle = blobHandle; }
+    void setBlobDataHandle(ExecutionContext*, PassRefPtr<BlobDataHandle>);
+    BodyStreamBuffer2* buffer() const { return m_buffer; }
     String mimeType() const { return m_mimeType; }
     void setMIMEType(const String& type) { m_mimeType = type; }
 
@@ -112,6 +115,7 @@ private:
     // FIXME: Support m_manualRedirectFlag;
     // FIXME: Support m_redirectCount;
     Tainting m_responseTainting;
+    Member<BodyStreamBuffer2> m_buffer;
     String m_mimeType;
 };