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 c0e63c873419c25b33fd0d8f0279e59503ee43e2..df148699820ef34f7cd6f598ba54f1c117d95645 100644
--- a/content/common/url_loader.mojom
+++ b/content/common/url_loader.mojom
@@ -59,6 +59,12 @@ interface URLLoaderClient {
   // 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);