From a recent review comment:

1) Place this string in components/autofill_strings.grdp

2) Let Android use it via formatter_data="android_java"

3) Remove IDS_PAYMENTS_ORDER_SUMMARY_LABEL from android_chrome_strings.grdp.

4) Use R.string.payment_request_order_summary_title instead of R.string.payments_order_summary_label in PaymentRequestUI.java.

5) Optional: Use IDS_PAYMENT_REQUEST_ORDER_SUMMARY_TITLE instead of IDS_IOS_PAYMENT_REQUEST_PAYMENT_ITEMS_TITLE.