Merge to XFA: Beef up app_props.in and tidy app.cpp.

Small manual edit in fpdfsdk/src/javascript/app.cpp

(cherry picked from commit b830fbc03a6d12d8b5be50e85499c281a4c5da7f)
Original Review URL: https://codereview.chromium.org/1317393003 .

R=thestig@chromium.org
TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1302423008 .