Discourse marker like is finding its way into usage guides, as Viktorija Kostadinova shows in her work. None of the usage guides in the HUGE database, all published before 2010, has an entry on like. But some writers do discuss it, even if only in passing, such as Caroline Taggart in Her Ladyship’s Guide to the Queen’s English (2010), and just now I found another one, entirely by chance (searching for the word like in the database is obviously an impossible job ).
I found the following reference in the Harper Dictionary of Contemporary Usage (Morris and Morris, 1975), as in Taggart’s case as part of the discussion of the use of like for as:
In a day when the young use either ‘like’ or ‘you know’ as meaningless punctuation in almost every sentence
So the discourse marker already attracted attention from usage commentators in the 1970s, and the person who commented on it here was George Cornish. I’ve no idea who he was (or what made him mention this particular feature), except that he was one of the panellists invoked by Morris and Morris for discussions about linguistic correctness, which they subsequently quoted in their book.