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

Source/modules/fetch/FetchBlobDataConsumerHandle.h

+// Copyright 2015 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.
+
+#ifndef FetchBlobDataConsumerHandle_h
+#define FetchBlobDataConsumerHandle_h
+
+#include "core/fetch/ResourceLoaderOptions.h"
+#include "core/loader/ThreadableLoader.h"
+#include "modules/fetch/FetchDataConsumerHandle.h"
+#include "platform/blob/BlobData.h"
+#include "wtf/PassOwnPtr.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefPtr.h"
+
+namespace blink {
+
+class ExecutionContext;
+class FetchBlobDataConsumerHandle final : public FetchDataConsumerHandle {
+public:
+    class LoaderFactory : public GarbageCollectedFinalized<LoaderFactory> {
+    public:
+        virtual PassRefPtr<ThreadableLoader> create(ExecutionContext&, ThreadableLoaderClient*, const ResourceRequest&, const ThreadableLoaderOptions&, const ResourceLoaderOptions&) = 0;
+        virtual ~LoaderFactory() { }
+        DEFINE_INLINE_VIRTUAL_TRACE() { }
+    };
+
+    static PassOwnPtr<FetchDataConsumerHandle> create(ExecutionContext*, PassRefPtr<BlobDataHandle>);
+
+    // For testing.
+    static PassOwnPtr<FetchDataConsumerHandle> create(ExecutionContext*, PassRefPtr<BlobDataHandle>, LoaderFactory*);
+
+    ~FetchBlobDataConsumerHandle();
+
+private:
+    FetchBlobDataConsumerHandle(ExecutionContext*, PassRefPtr<BlobDataHandle>, LoaderFactory*);
+    Reader* obtainReaderInternal(Client*) override;
+
+    const char* debugName() const override { return "FetchBlobDataConsumerHandle"; }
+
+    class ReaderContext;
+    RefPtr<ReaderContext> m_readerContext;
+};
+
+} // namespace blink
+
+#endif // FetchBlobDataConsumerHandle_h