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
+        // throughWebDataConsumerHandle APIs without calling this function.

[yhirano, 2015/06/17 04:13:34]

space after "through"

[hiroshige, 2015/06/17 08:30:23]

Done.

+        virtual PassRefPtr<BlobDataHandle> blobDataHandle() = 0;

[yhirano, 2015/06/17 04:13:35]

As this function is not a getter, a name that doesn't sound like a getter is
preferable, I think?

[hiroshige, 2015/06/17 08:30:23]

Hmm. Do you have suggestions for the name?
(|obtainBlobDataHandle|?)

[yhirano, 2015/06/17 09:10:16]

take / obtain / acquire?

[hiroshige, 2015/06/17 09:25:26]

Done in Patch Set 9.

+    };
+    PassOwnPtr<Reader> obtainReader(Client* client) { return adoptPtr(obtainReaderInternal(client)); }

[yhirano, 2015/06/17 04:13:35]

Please say that obtainReader is non-virtual overriding, which is OK in this
case.
(I will make it virtual when we can use scoped_ptr / unique_ptr in both blink
and chromium).

[hiroshige, 2015/06/17 08:30:23]

Done.

+
+private:
+    Reader* obtainReaderInternal(Client*) override = 0;
+};
+
+} // namespace blink
+
+#endif // FetchDataConsumerHandle_h