What is the history of the white chocolate macadamia nut cookie?
I'm not certain of this answer, but if I had to make a bet, I think the cookie at least was popularized, if not originated completely, with Debbi Fields of Mrs. Fields' Original Cookies.

Macadamia nuts appeared in pairings with (milk or dark) chocolate, usually just in chocolate-covered versions or chunks of nuts in chocolate going back to at least the 1970s.  While I could find sporadic references to macadamia use in baked goods, I couldn't find any references specifically to white chocolate and macadamia in this era.

Macadamia nuts were an unusual ingredient in the 1980s (often associated in the U.S. with Hawaii), but Mrs. Fields' cookies began using them, perhaps due to the connection of the company in one of its earliest store locations in Honolulu during its initial expansion in 1980.  At some point in the 1980s, several macadamia nut flavored cookies were introduced by Mrs. Fields, including pairings with semisweet chocolate, coconut, and white chunk with macadamia nuts.  This page indicates that the white chocolate flavor was available by 1987.

But what evidence is there that Mrs. Fields in particular popularized this flavor?  Well, I could find no references to this pairing before 1987, when we know these cookies were sold by Mrs. Fields.  However, Mrs. Fields didn't just stop with cookies: in 1986-87, in addition to chocolate-dipped macadamia nuts, it tried to introduce ice cream with chocolate and macadamia nuts and even chocolate chip-macadamia soda.  The Mrs. Fields company seemed obsessed with macadamia-chocolate items at this time.  A Hawaiian book in 1988 could immediately make the association from macadamia nuts to Mrs. Fields, stating that:


  Macadamia-nut pie and macadamia-nut ice cream have become Hawaiian
  classics.  Famous Amos' and Mrs. Fields' macadamia chocolate chip
  cookies would not be nearly as good with any other nut.


While both Famous Amos and Mrs. Fields apparently had macadamia cookies by this time, it was the white chocolate chunk version by Mrs. Fields that seems to have brought a new wave with it.

All other references outside Mrs. Fields to specific pairing of white chocolate and macadamia nuts date to the late 1980s or later.  The earliest references I can find in Google appear in ice cream flavors (see this LA Times article from 1988), but there also appears to be a trend in brownies made with white chocolate and macadamia nuts around this time, as in the first mention of the pairing in the NY Times in 1989 as well as this AP reference in 1990 to white chocolate macadamia nut brownies.  One also begins to see references to cheesecake (NY Times, 1990) and tarts (NY Times, 1992) flavored in the same way at upscale restaurants.  One of the earliest references Google seems to find for cookies is in 1993, where the Chicago Tribune covers a designer of high-end gift baskets, several of which seem to include white chocolate macadamia nut cookies. 

After an initial period when the flavor pairing was apparently associated with higher-end cuisine and cookies, it began to spread more widely.  By the mid-1990s, the white chocolate macadamia fad was in full swing, as the Washington Post could announce in 1996 that the most recent Joy of Cooking Christmas Cookies book contained recipes for "monster-size cookies in trendy flavors such as mocha walnut and white chocolate macadamia."

In any case, I don't have clear evidence that the cookie flavor pairing originated with Mrs. Fields, but it seems likely to have been popularized by that company in the late 1980s and early 1990s.

EDIT: Further evidence from Google Ngram of the popularity of the phrase "white chocolate macadamia" beginning its rise in 1987 through the mid-1990s, so at least we can narrow down the time period.