Are there libraries or techniques for 'noisifying' text data?
I you want some kind of data-sets like Google spell checking data I suggest you look into the The WikEd Error Corpus dataset. The corpus consists of more than 12 million sentences with a total of 14 million edits of various types, this edits include: spelling error corrections, grammatical error corrections, stylistic changes. All these from the Wikipedia correction history. The owners (authors) of the data-set describe the data mining process in this paper. Also check this question in quora it contains links to various data-sets with spelling errors. Finally this page can also be useful.