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<  * @param {EventListener|function(!Event):(boolean|undefined)} listener
---
>  * @param {EventListener} listener
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<  * @param {EventListener|function(!Event):(boolean|undefined)} listener
---
>  * @param {EventListener} listener

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<  * @param {EventListener|function(!Event):*} listener
---
>  * @param {EventListener} listener
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<  * @param {EventListener|function(!Event):*} listener
---
>  * @param {EventListener} listener

Allow add/removeEventListener callbacks to return any type
Allow add/removeEventListener callbacks to return any type

Unlike DOM0 event listeners (e.g. using .onClick), where returning false
prevents the default action, event handlers added with add/removeEventListener can return anything without any behavioral changes.
http://blog.niftysnippets.org/2011/11/story-on-return-false.html

The primary motivation for this change is allowing passing async functions to add/removeEventListener.

PiperOrigin-RevId: 221282023
