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For Grid View, add titles "Folders" and "Files" for the respective
sections.

Add test to check that the title is available.

Add translations and their screenshots.

Test: browser_tests --gtest_filter="*showGridViewTitles*"
Bug: 992822
Change-Id: Ic71d31891e2d8575920fa815b0a9df5e49bc5ddb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2087231
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747085}