Add method to abort Stream construction to BlobRegistry

public/platform/WebBlobRegistry.h

Index: public/platform/WebBlobRegistry.h
diff --git a/public/platform/WebBlobRegistry.h b/public/platform/WebBlobRegistry.h
index 726c522044f38f1fa8d89eed2de43a9bba470b96..cc41b00eacaf464cff2a78c38ec6c4ba39715242 100644
--- a/public/platform/WebBlobRegistry.h
+++ b/public/platform/WebBlobRegistry.h
@@ -67,9 +67,14 @@ public:
     // Add data to the stream referred by the URL.
     virtual void addDataToStream(const WebURL&, WebThreadSafeData&) { WEBKIT_ASSERT_NOT_REACHED(); }
 
-    // Tell the registry that this stream won't receive any more data.
+    // Tell the registry that construction of this stream has completed
+    // successfully and so it won't receive any more data.
     virtual void finalizeStream(const WebURL&) { WEBKIT_ASSERT_NOT_REACHED(); }
 
+    // Tell the registry that construction of this stream has been aborted and
+    // so it won't receive any more data.
+    virtual void abortStream(const WebURL&) { WEBKIT_ASSERT_NOT_REACHED(); }
+
     // Unregisters a stream referred by the URL.
     virtual void unregisterStreamURL(const WebURL&) { WEBKIT_ASSERT_NOT_REACHED(); }
 };