Observe CXFA_FFPageView across OnSetFocus() events.

CXFA_FFPageView object is destroyed by JS code of enter event.
Use ObservedPtr to catch this destruction.

Bug: chromium:982397
Change-Id: Ie7cd472f561eec410c9ccd5a25319fbd8e63b5ec
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/58390
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
diff --git a/AUTHORS b/AUTHORS
index bd3e4bd..3c97237 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -33,6 +33,7 @@
 Matt Giuca <mgiuca@chromium.org>
 Michael Doppler <m.doppler@gmail.com>
 Miklos Vajna <vmiklos@vmiklos.hu>
+Minh Trần <myoki.crystal@gmail.com>
 Nico Weber <thakis@chromium.org>
 Nicolás Peña <npm@chromium.org>
 Peter Kasting <pkasting@chromium.org>