Add success dialog after key backup (#10177)

src/components/views/dialogs/BaseDialog.tsx

@@ -50,6 +50,9 @@ interface IProps extends IDialogProps {
     // determine its size. Default: true.
     "fixedWidth"?: boolean;
 
+    // To be displayed at the top of the dialog. Even above the title.
+    "top"?: React.ReactNode;
+
     // Title for the dialog.
     "title"?: JSX.Element | string;
     // Specific aria label to use, if not provided will set aria-labelledBy to mx_Dialog_title
@@ -161,6 +164,7 @@ export default class BaseDialog extends React.Component<IProps> {
                         mx_Dialog_fixedWidth: this.props.fixedWidth,
                     })}
                 >
+                    {this.props.top}
                     <div
                         className={classNames("mx_Dialog_header", {
                             mx_Dialog_headerWithButton: !!this.props.headerButton,