This has happened on my home pc and now my work PC.
avast! removes adobe pdf from internet explorer (pops up with the suggestion as it has a poor rating), during the uninstall it asks for a new default search engine (why?) then the Google chrome app launcher only loads chrome with msn page direct, it doesn’t show the chrome apps in it’s normal window.
Like I say it’s happened twice on two different pc’s ( both Windows 7 sp1) but didn’t realise the same chain of events effected the chrome app until the second time around!