Hard-code modifier key codes since the header file that defines them was not merged.
Hard-code modifier key codes since the header file that defines them was not merged.

BUG=492808
R=garykac@chromium.org

Review URL: https://codereview.chromium.org/1150383005

Cr-Commit-Position: d34a0005849006230ae7ffb1a9693419810a06bc@{#207}
Cr-Branched-From: 40cda19e609fd36fbf5fe489055423e611631abc@{#330231}

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