Files App: Add a flag for rename feature to flag descriptions

This CL adds a flag that enables external drive rename action in the
context menu. The flag is added to flag descriptions and as a result, it
is visible under chrome://flags.

BUG=274041

Change-Id: Ia83b12daab124b0f664699b432d48c6138410678
Reviewed-on: https://chromium-review.googlesource.com/644667
Reviewed-by: Naoki Fukino <fukino@chromium.org>
Commit-Queue: Klemen Kozjek <klemenko@google.com>
Cr-Original-Commit-Position: refs/heads/master@{#499134}(cherry picked from commit f2b30e45756aac3dcdcef7ef13834c0601b4553a)
Reviewed-on: https://chromium-review.googlesource.com/662478
Cr-Commit-Position: refs/branch-heads/3202@{#154}
Cr-Branched-From: fa6a5d87adff761bc16afc5498c3f5944c1daa68-refs/heads/master@{#499098}
4 files changed