XFA: merge patch from CL 733693003, get rid of FX_LPCSTR cast

Get rid of FX_LPCSTR cast.

Follow up on https://codereview.chromium.org/733693003

R=brucedawson@chromium.org, tsepez@chromium.org

Review URL: https://codereview.chromium.org/809993004
27 files changed