Implement upload progress handling in Mojo loading

content/common/url_loader.mojom

 // Copyright 2016 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.
 
 module content.mojom;
 
 [Native]
 struct URLRequest;
 
 [Native]
@@ skipping 41 matching lines @@
   // |report_raw_headers| is set and |download_to_file| is unset in the request.
   // The transfer size is the length of the response (including both headers
   // and the body) over the network. |transfer_size_diff| is the difference from
   // the value previously reported one (including the one in OnReceiveResponse
   // and OnReceiveRedirect). It must be positive.
   // TODO(yhirano): Dispatch this notification even when |download_to_file| is
   // set.
   // TODO(yhirano): Consider using an unsigned type.
   OnTransferSizeUpdated(int32 transfer_size_diff);
 
+  // Called when the service made some progress on the file upload. This is
+  // called only when the request has an upload data.
+  // Call the response closure when the client is ready to receive the next
+  // upload progress.
+  OnUploadProgress(int64 current_position, int64 total_size) => ();
+
   // Called when the loader starts loading response body.
   OnStartLoadingResponseBody(handle<data_pipe_consumer> body);
 
   // Called when the loading completes. No notification will be dispatched for
   // this client after this message arrives.
   OnComplete(URLLoaderStatus completion_status);
 };