GitLab

This cl adds a '+' icon between the bubble views of modifiers and key in
the Keyboard Shortcut Viewer (KSV).

Changes:
1. ui::VKEY_UNKNOWN is used as a separator indicator and will be shown
as a highlighted "+" icon.
2. Insert the ui::VKEY_UNKNOWN into |shortcut_key_codes| as the separator.
3. Replace the separator with '+' icon when creating
KeyboardShortcutItemView.

Bug: 768932
Test: Manually test that the separator icon is correctly created.
Change-Id: I2d01beb3f4c4b69a18cbb4820afc024f92679dc3
Reviewed-on: https://chromium-review.googlesource.com/912135Reviewed-by: Mitsuru Oshima (In Tokyo) <oshima@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536949}