Recall that Google recently changed the "+" operator in search from forcing inclusion of a search term to "Google+ Direct Connect" [1]. The removal of the "+" from the Chrome new tab button is simply another step toward focusing the "+" symbol on the Google+ brand. I would expect to see something like a Google+ toolbar baked into Chrome in the not-too-distant future.
[1] http://support.google.com/plus/bin/answer.py?hl=en&answe...