Merge to XFA: Tidy up CPDFDOC_Environment.

Original Review URL: https://codereview.chromium.org/1235393002 .
(cherry picked from commit fb07e2843dad0774d5842c2b08e7792164efc14a)

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1244503002 .
10 files changed