exo: Do not send the key event already consumed by the system IME.
exo: Do not send the key event already consumed by the system IME.

When a key event is filtered by IME, its key_code() is masked by VKEY_PROCESSKEY
but code() is kept as-is. Such a filtered key event should not be sent to the
client in unmasked form. Otherwise the event is double-handled.

BUG=597197

Review URL: https://codereview.chromium.org/1828643002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#382839}

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