Advanced URL Shortener add-on for Google Docs lets you to shorten/expand multiple long/short URLs in your Doc by using bitly service.

Free Features:
 - Shorten/Expand a single link at a time
 - Click summary of a single link at a time

Premium Features:
 - Shorten/Expand selected/all links in the Doc
 - Get click summary of selected/all bitly links in the Doc

IMPORTANT: 

Further, The volume of URLs that can be converted depends on your Bitly account type and account limits

Bitly Enterprise
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 * Shorten up to 50,000 links per minute.
 * Monthly maximum is determined by the terms of the Enterprise account.

Bitly Free
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* Shorten up to 10,000 links per minute.
* Monthly maximum is 10,000 links per month.

Bitly institutes per-month, per-hour, per-minute, per-user, and per-IP rate limits.
    10,000 new Bitlinks created per month
    1,000 calls per hour
    100 calls per minute

For more details visit: https://dev.bitly.com/rate_limiting.html