[Fetch] Support various operations after reading data partially.

Source/modules/fetch/Body.h

 // Copyright 2014 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 Body_h
 #define Body_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "bindings/core/v8/ScriptWrappable.h"
@@ skipping 38 matching lines @@
     ReadableStream* body();
 
     // Sets the bodyUsed flag to true. This signifies that the contents of the
     // body have been consumed and cannot be accessed again.
     void setBodyUsed();
     bool bodyUsed() const;
 
     bool streamAccessed() const;
 
     // Creates a new BodyStreamBuffer to drain the data from the ReadableStream.
-    BodyStreamBuffer* createDrainingStream(bool* dataLost);
+    BodyStreamBuffer* createDrainingStream();
 
     // ActiveDOMObject override.
     virtual void stop() override;
     virtual bool hasPendingActivity() const override;
 
     DECLARE_VIRTUAL_TRACE();
 
 protected:
     // Copy constructor for clone() implementations
     explicit Body(const Body&);
@@ skipping 31 matching lines @@
     ResponseType m_responseType;
     RefPtrWillBeMember<ScriptPromiseResolver> m_resolver;
     Member<ReadableStreamSource> m_streamSource;
     Member<ReadableStreamImpl<ReadableStreamChunkTypeTraits<DOMArrayBuffer>>> m_stream;
     Member<ReadableStreamReader> m_streamReader;
 };
 
 } // namespace blink
 
 #endif // Body_h