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 f1b4d4252fa962452cc0869912df7402f1199bde..a20e70ae385b5d87c7a5e31fb30dcc8cab052a38 100644
--- a/content/common/url_loader.mojom
+++ b/content/common/url_loader.mojom
@@ -48,6 +48,12 @@ interface URLLoaderClient {
   // instead.
   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 cached metadata from a resource request is ready.
   OnReceiveCachedMetadata(array<uint8> data);