We saw a ZIP file created on macOS stores file names in UTF-8 encoding
but the language encoding flag in the general purpose bit is not set.
This change will cover some of such cases when the encoding detector
detected that encoding.

Bug: 903664
Test: browser_tests --gtest_filter=ZipFiles/FilesAppBrowserTest.Test/*
Test: manually verified using the ZIP attached to the bug
Change-Id: I5ef488cf5a0ba04feee9e8d2025054e16785f832
Reviewed-on: https://chromium-review.googlesource.com/c/1328623Reviewed-by: Anand Mistry <amistry@chromium.org>
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607141}