Introduce FetchFormDataConsumerHandle.

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 "modules/ModulesExport.h"
 #include "platform/blob/BlobData.h"
+#include "platform/network/FormData.h"
 #include "public/platform/WebDataConsumerHandle.h"
 #include "wtf/Forward.h"
 #include "wtf/PassRefPtr.h"
 
 namespace blink {
 
 // 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
@@ skipping 13 matching lines @@
         // Drains the data as a BlobDataHandle.
         // If this function returns non-null BlobDataHandle:
         // - The bytes that will be read from the returned BlobDataHandle
         //   must be idential to the bytes that would be read through
         //   WebDataConsumerHandle::Reader APIs without calling this function.
         // - Subsequent calls to read() / beginRead() return |Done|.
         // This function can return |nullptr|, and in such cases this
         // function is no-op.
         // This function returns |nullptr| when called during two-phase read.
         virtual PassRefPtr<BlobDataHandle> drainAsBlobDataHandle(BlobSizePolicy = DisallowBlobWithInvalidSize) { return nullptr; }
+
+        // Drains the data as a FormData.
+        // This function returns a non-null form data when
+        // - The handle is made from a FormData-convertible type,
+        // - The reader is running on a suitable thread

[hiroshige, 2015/08/10 13:27:03]

nit: append ", and" at the end of line?

[yhirano, 2015/08/11 06:08:43]

Done.

+        // - No data is read yet.
+        // After that read() / beginRead() will return |Done|.
+        // Otherwise this function does nothing and returns null.
+        // This function returns |nullptr| when called during two-phase read.
+        virtual PassRefPtr<FormData> drainAsFormData() { return nullptr; }
     };
 
     // 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