Add a callback for cancelling the context menu.
Add a callback for cancelling the context menu.

The callback updates the |visible| property to NO so clients can
correctly determine if the context menu has been dismissed.

BUG=489121

Review URL: https://codereview.chromium.org/1144873002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#330562}

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