Introduce FetchFormDataConsumerHandle.

Source/modules/fetch/FetchBlobDataConsumerHandle.cpp

Index: Source/modules/fetch/FetchBlobDataConsumerHandle.cpp
diff --git a/Source/modules/fetch/FetchBlobDataConsumerHandle.cpp b/Source/modules/fetch/FetchBlobDataConsumerHandle.cpp
index 9005fb551944f0fc283f8c371eaa5be99f5a03fb..27ef84237f77002d6036e6a7f0876cbbc568c9aa 100644
--- a/Source/modules/fetch/FetchBlobDataConsumerHandle.cpp
+++ b/Source/modules/fetch/FetchBlobDataConsumerHandle.cpp
@@ -390,6 +390,16 @@ public:
             return blobDataHandle.release();
         }
 
+        PassRefPtr<FormData> drainAsFormData() override
+        {
+            RefPtr<BlobDataHandle> handle = drainAsBlobDataHandle(AllowBlobWithInvalidSize);
+            if (!handle)
+                return nullptr;
+            RefPtr<FormData> formData = FormData::create();
+            formData->appendBlob(handle->uuid(), handle);
+            return formData.release();
+        }
+
     private:
         RefPtr<ReaderContext> m_readerContext;
         OwnPtr<WebDataConsumerHandle::Reader> m_reader;