diff --git a/mock_http_fetcher.h b/mock_http_fetcher.h
index 6d72b92..0fd9537 100644
--- a/mock_http_fetcher.h
+++ b/mock_http_fetcher.h
@@ -51,6 +51,11 @@
       delegate_->SeekToOffset(offset);
   }
 
+  // Dummy: no bytes were downloaded.
+  virtual size_t GetBytesDownloaded() {
+    return sent_size_;
+  }
+
   // Begins the transfer if it hasn't already begun.
   virtual void BeginTransfer(const std::string& url);