Merge to XFA: Introduce CPDF_DocumentFromFPDFDocument().

Manual merges everywhere.

Original Review URL: https://codereview.chromium.org/1395493007 .
(cherry picked from commit bb51c4fb6bc6095984c303c95e5336f83e66bc67)

Original Review URL: https://codereview.chromium.org/1396283006 .
(cherry picked from commit 86adb658843658969041a13bf6cf0cc950ffe8ed)

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1395353004 .
8 files changed