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This cl adds all shortcuts metadata and strings for Keyboard Shortcut
Viewer (KSV).

Bug: 768932
Test: KeyboardShortcutViewerMetadataTest and Manually tested on device
Change-Id: I0dc85fa4bffb5a9a1f19b86e991faf7b13b75a93
Reviewed-on: https://chromium-review.googlesource.com/922389
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537415}