Change BodyStreamBuffer to be FetchDataConsumerHandle-based and enable backpressure in Fetch API

Source/modules/fetch/FetchDataLoader.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 FetchDataLoader_h
 #define FetchDataLoader_h
 
 #include "core/dom/DOMArrayBuffer.h"
+#include "core/streams/Stream.h"
 #include "modules/fetch/FetchDataConsumerHandle.h"
 #include "platform/blob/BlobData.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
 
 namespace blink {
 
 // FetchDataLoader subclasses
 // 1. take a reader of FetchDataConsumerHandle |handle|,
 // 2. read all data, and
@@ skipping 17 matching lines @@
             ASSERT_NOT_REACHED();
         }
         virtual void didFetchDataLoadedArrayBuffer(PassRefPtr<DOMArrayBuffer>)
         {
             ASSERT_NOT_REACHED();
         }
         virtual void didFetchDataLoadedString(const String&)
         {
             ASSERT_NOT_REACHED();
         }
+        virtual void didFetchDataLoadedStream()
+        {
+            ASSERT_NOT_REACHED();
+        }
 
         virtual void didFetchDataLoadFailed() = 0;
 
         DEFINE_INLINE_VIRTUAL_TRACE() { }
     };
 
     static FetchDataLoader* createLoaderAsBlobHandle(const String& mimeType);
     static FetchDataLoader* createLoaderAsArrayBuffer();
     static FetchDataLoader* createLoaderAsString();
+    static FetchDataLoader* createLoaderAsStream(Stream* outStream);
 
     virtual ~FetchDataLoader() { }
 
     // start() should be called only once on the created thread.
     // start() do not take the ownership of |handle|.
     // |handle| must not be locked when called.
     virtual void start(FetchDataConsumerHandle* /* handle */, Client*) = 0;
 
     virtual void cancel() = 0;
 
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 };
 
 } // namespace blink
 
 #endif // FetchDataLoader_h