libsysprof-analyze: track relative offset for frame

This is handy so that we don't have to keep multiple objects around to
handle this request. Otherwise we'd need to keep references to the
document and that is a bit annoying.

This of course has a limit of about an hour (in tv_nsec), but that is
far longer than we can realistically record anyway.

src/libsysprof-analyze/sysprof-document.c

@@ -118,7 +118,8 @@ sysprof_document_get_item (GListModel *model,
   ret = _sysprof_document_frame_new (self->mapped_file,
                                      (gconstpointer)&self->base[ptr->offset],
                                      ptr->length,
-                                     self->needs_swap);
+                                     self->needs_swap,
+                                     self->header.time);
 
   /* Annotate processes with pre-calculated info */
   if (SYSPROF_IS_DOCUMENT_PROCESS (ret))