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This cl makes some string changes for Keyboard Shortcuts Viewer based on
TC.

Bug: 833967, b/77166809, b/77861902
Test: manual
Change-Id: Ib28c40c1aea1303151bf2f4a687df7f230760cfa
Reviewed-on: https://chromium-review.googlesource.com/1015601Reviewed-by: Qiang Xu <warx@google.com>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551480}