Suppress MissingSuperCall error in DownloadActivity.onRequestPermissionsResult

@CallSuper was added to FragmentActivity.onRequestPermissionsResult in
r.android.com/1233518, which is present in the AndroidX fragment library
v1.2. This change will prevent a compilation error when upgrading to
that version of the library.

Bug: 1123216
Change-Id: Icef9c868cc5cf2de38b6c40cacdc91f48e1edfbe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2386277


Commit-Queue: Min Qin <qinmin@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804414}