Add FetchDataConsumerHandle and utility functions/classes

Source/modules/fetch/DataConsumerHandleUtil.h

Index: Source/modules/fetch/DataConsumerHandleUtil.h
diff --git a/Source/modules/fetch/DataConsumerHandleUtil.h b/Source/modules/fetch/DataConsumerHandleUtil.h
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+++ b/Source/modules/fetch/DataConsumerHandleUtil.h
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+// 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 DataConsumerHandleUtil_h
+#define DataConsumerHandleUtil_h
+
+#include "modules/fetch/FetchDataConsumerHandle.h"
+#include "public/platform/WebDataConsumerHandle.h"
+#include "wtf/PassOwnPtr.h"
+#include "wtf/WeakPtr.h"
+
+namespace blink {
+
+// Returns a handle that returns ShouldWait for read / beginRead and
+// UnexpectedError for endRead.
+PassOwnPtr<WebDataConsumerHandle> createWaitingDataConsumerHandle();
+
+// Returns a handle that returns Done for read / beginRead and
+// UnexpectedError for endRead.
+PassOwnPtr<WebDataConsumerHandle> createDoneDataConsumerHandle();
+
+// Returns a handle that returns UnexpectedError for read / beginRead /
+// endRead.
+PassOwnPtr<WebDataConsumerHandle> createUnexpectedErrorDataConsumerHandle();
+
+// Returns a FetchDataConsumerHandle that wraps WebDataConsumerHandle.
+PassOwnPtr<FetchDataConsumerHandle> createFetchDataConsumerHandleFromWebHandle(PassOwnPtr<WebDataConsumerHandle>);
+
+// A helper class to call Client::didGetReadable() asynchronously after
+// Reader creation.
+// NotifyOnReaderCreationHelper must be owned by a reader and
+// |client| must be the client of the reader.
+class NotifyOnReaderCreationHelper final {
+public:
+    NotifyOnReaderCreationHelper(WebDataConsumerHandle::Client* /* client */);
+
+private:
+    void notify(WebDataConsumerHandle::Client*);
+
+    WeakPtrFactory<NotifyOnReaderCreationHelper> m_factory;
+};
+
+} // namespace blink
+
+#endif // DataConsumerHandleUtil_h