Add FetchDataConsumerHandle and utility functions/classes

Source/modules/fetch/FetchDataConsumerHandle.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 FetchDataConsumerHandle_h
+#define FetchDataConsumerHandle_h
+
+#include "public/platform/WebDataConsumerHandle.h"
+#include "wtf/Forward.h"
+#include "wtf/PassRefPtr.h"
+
+namespace blink {
+
+class BlobDataHandle;
+
+// This is an interface class that adds Reader's blobDataHandle() to
+// WebDataConsumerHandle.
+// This class works not very well with Oilpan: As this class is not garbage
+// collected while many clients or related objects may be, it is very easy
+// to create a reference cycle. When an client is garbage collected, making
+// the client own the handle is the right way.
+class FetchDataConsumerHandle : public WebDataConsumerHandle {
+public:
+    class Reader : public WebDataConsumerHandle::Reader {
+    public:
+        // Returns a blob handle representing the body data. This function can
+        // returns null when the object doesn't have such a handle. Calling
+        // this function drains the body data.
+        // This function is defined for performance. If this function returns a
+        // non-null handle, the bytes that will be read from the handle must be
+        // idential to the bytes that will be read
+        // through WebDataConsumerHandle APIs without calling this function.
+        virtual PassRefPtr<BlobDataHandle> blobDataHandle() = 0;
+    };
+
+    // TODO(yhirano): obtainReader() is currently non-virtual override, and
+    // will be changed into virtual override when we can use scoped_ptr /
+    // unique_ptr in both Blink and Chromium.
+    PassOwnPtr<Reader> obtainReader(Client* client) { return adoptPtr(obtainReaderInternal(client)); }
+
+private:
+    Reader* obtainReaderInternal(Client*) override = 0;
+};
+
+} // namespace blink
+
+#endif // FetchDataConsumerHandle_h