eventSender.beginDragWithFiles drags with wrong paths from http tests The new eventSender.beginDragWithFiles takes relative paths. These are resolved against the loaded document. When you run an http test, the path passed to DumpRenderTree is a URL pointing to localhost, so the to-be-dragged files are also urls pointing to local host. We can't stat non-file urls, so the stat fails and File.fileSize returns 0. The only way I can think to fix this is if we pass some sort of absolute path to DumpRenderTree in addition to the http://localhost test url, so that DRT can know how to resolve these paths to on-disk files for dragging.
This support was added in bug 25852.
We can work around this limitation for the moment using http/local tests. http/local tests are loaded as normal on-disk tests, but the http server is running. So we can have them load remote iframes off of localhost/