Add missing definitions in MessageSender externs.
Add missing definitions in MessageSender externs.

There are a few missing definitions for MessageSender in chrome externs.
https://developer.chrome.com/extensions/runtime#type-MessageSender

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=289391811

Yannic/closure-compiler,Yannic/closure-compiler,google/closure-compiler,vobruba-martin/closure-compiler,Yannic/closure-compiler,Yannic/closure-compiler,monetate/closure-compiler,google/closure-compiler,google/closure-compiler,vobruba-martin/closure-compiler,monetate/closure-compiler,google/closure-compiler,vobruba-martin/closure-compiler,nawawi/closure-compiler,monetate/closure-compiler,monetate/closure-compiler,ChadKillingsworth/closure-compiler,ChadKillingsworth/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler,nawawi/closure-compiler,vobruba-martin/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler