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 17af152dd8b4b296c2656a335a607fc93d95c9ba..5429331b06064cda930e9b515472a357b57b85fa 100644
--- a/content/common/url_loader.mojom
+++ b/content/common/url_loader.mojom
@@ -49,6 +49,12 @@ 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.
+  // The implementation should 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);