URLFetcher won't call delegate until file is closed.

net/base/file_stream.h

Index: net/base/file_stream.h
diff --git a/net/base/file_stream.h b/net/base/file_stream.h
index 0fb3fb265697f317df69a0915979035bd2970461..89ab01506ee5fbc166c020876c78fde9ef4eef07 100644
--- a/net/base/file_stream.h
+++ b/net/base/file_stream.h
@@ -81,6 +81,11 @@ class NET_EXPORT FileStream {
   // automatically closed when FileStream is destructed.
   virtual int OpenSync(const base::FilePath& path, int open_flags);
 
+  // Closes the file. If the file is open asynchronously, returns ERR_IO_PENDING
+  // and closes the file asynchronously, calling |callback| when done.
+  // Otherwise, closes the file immediately and returns OK.
+  virtual int Close(const CompletionCallback& callback);
+
   // Returns true if Open succeeded and Close has not been called.
   virtual bool IsOpen() const;