Revert of Some linked_ptr removal in chromeos file_browser_handler. (patchset #5 id:80001 of https://codereview.chromium.org/2707193005/ )

Reason for revert:
This might be the cause of crash: crbug/696375

Original issue's description:
> Some linked_ptr removal in chromeos file_browser_handler.
>
> BUG=556939
>
> Review-Url: https://codereview.chromium.org/2707193005
> Cr-Commit-Position: refs/heads/master@{#453064}
> Committed: https://chromium.googlesource.com/chromium/src/+/37ab3be841440d4ec5abf1160acf32c905796d13

TBR=hirono@chromium.org,lazyboy@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=556939

Review-Url: https://codereview.chromium.org/2717213002
Cr-Commit-Position: refs/heads/master@{#453134}
6 files changed