autofill::mojom::FormData is received in the browser process by autofill::mojom::AutofillDriver which is associated with a specific RenderFrameHost.  Therefore, instead of receiving autofill::mojom::FormData::origin over IPC, the browser should be able to calculate it from render_frame_host->GetLastCommittedURL().

Note: |origin| here is not url::Origin, but rather document GURL stripped of auth and params - see GetCanonicalOriginForDocument for more details.