Implement BodyStreamBuffer::create() from WebDataConsumerHandle

Source/modules/fetch/BodyStreamBuffer.h

Index: Source/modules/fetch/BodyStreamBuffer.h
diff --git a/Source/modules/fetch/BodyStreamBuffer.h b/Source/modules/fetch/BodyStreamBuffer.h
index f7d37a16f7d5640feaba7785dd73257f32a98b8f..cdb47baab116261c68167786d96f4c924f8e15d1 100644
--- a/Source/modules/fetch/BodyStreamBuffer.h
+++ b/Source/modules/fetch/BodyStreamBuffer.h
@@ -9,6 +9,7 @@
 #include "modules/ModulesExport.h"
 #include "platform/blob/BlobData.h"
 #include "platform/heap/Heap.h"
+#include "public/platform/WebDataConsumerHandle.h"
 #include "wtf/Deque.h"
 #include "wtf/RefPtr.h"
 #include "wtf/text/WTFString.h"
@@ -71,6 +72,11 @@ public:
     bool isObserverRegistered() const { return m_observer.get(); }
     DECLARE_TRACE();
 
+    // Creates a BodyStreamBuffer from |handle| as the source.
+    // On failure, BodyStreamBuffer::error() is called with a NetworkError
+    // with |failureMessage|.
+    static BodyStreamBuffer* create(PassOwnPtr<WebDataConsumerHandle> /* handle */, const String& failureMessage);
+
 private:
     Deque<RefPtr<DOMArrayBuffer>> m_queue;
     bool m_isClosed;