Introduce FetchFormDataConsumerHandle.

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/ModulesExport.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;
+// A FetchBlobDataConsumerHandle is created from a blob handle and it will
+// return a valid handle from drainAsBlobDataHandle as much as possible.
 class MODULES_EXPORT FetchBlobDataConsumerHandle final : public FetchDataConsumerHandle {
     WTF_MAKE_NONCOPYABLE(FetchBlobDataConsumerHandle);
 public:
     class MODULES_EXPORT LoaderFactory : public GarbageCollectedFinalized<LoaderFactory> {
     public:
         virtual PassRefPtr<ThreadableLoader> create(ExecutionContext&, ThreadableLoaderClient*, const ResourceRequest&, const ThreadableLoaderOptions&, const ResourceLoaderOptions&) = 0;
         virtual ~LoaderFactory() { }
         DEFINE_INLINE_VIRTUAL_TRACE() { }
     };
 
@@ skipping 10 matching lines @@
 
     const char* debugName() const override { return "FetchBlobDataConsumerHandle"; }
 
     class ReaderContext;
     RefPtr<ReaderContext> m_readerContext;
 };
 
 } // namespace blink
 
 #endif // FetchBlobDataConsumerHandle_h