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If there is a hang-up in the Finalize() method for cast_service,
then the cast_shell process will never return and cannot be stopped
using SIGTERM. We should add a timeout so that the process is
forcibly killed if it refuses to exit properly.

BUG=

Review URL: https://codereview.chromium.org/1002603006

Cr-Commit-Position: refs/heads/master@{#322038}