Implement upload progress handling in Mojo loading

content/common/url_loader.mojom

Index: content/common/url_loader.mojom
diff --git a/content/common/url_loader.mojom b/content/common/url_loader.mojom
index f77988b238bd2d74a1d6a29e8b682de11ce9bec8..6e6d5a28fdb8fa091131b9ce7a4b87b3121f03f3 100644
--- a/content/common/url_loader.mojom
+++ b/content/common/url_loader.mojom
@@ -46,6 +46,12 @@ interface URLLoaderClient {
   // OnStartLoadingResponseBody in the call sequence in that case.
   OnDataDownloaded(int64 data_length, int64 encoded_length);
 
+  // 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);