[M131] Fix an issue that a null callback is passed when hitting

back/forward button on PDF

the callback is moved, so changing the code order to avoid using a null cb

(cherry picked from commit 6567bbee)

Low-Coverage-Reason: TRIVIAL_CHANGE
Bug: 377301543
Change-Id: I296466d6873e7f2edf9746717585273670e0ce5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5988331


Reviewed-by: Shu Yang <shuyng@google.com>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1377757}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5989723


Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Shu Yang <shuyng@google.com>
Cr-Commit-Position: refs/branch-heads/6778@{#1725}
Cr-Branched-From: b21671ca-refs/heads/main@{#1368529}