Fixup formfiller cleanup
Fixup formfiller cleanup

The CFFL_InteractiveFormFiller must be cleaned up before the environment because
the destruction of the formfiller will trigger the destruction of the formfiller
widgets. Some of those widgets may require stopping timers, which requires
accessing the environment.

BUG=chromium:654272, chromium:653459

Review-Url: https://codereview.chromium.org/2408163003

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium