Fix the System Profile to not load extensions. It could otherwise be forced to by GPO.

chrome/test/base/testing_profile_manager.cc

Index: chrome/test/base/testing_profile_manager.cc
diff --git a/chrome/test/base/testing_profile_manager.cc b/chrome/test/base/testing_profile_manager.cc
index 46ec927ee9b6c90a432efe9c49d0e91135a33443..0ae9f9995f88fd0ae830221b7029d46e8ce37eb6 100644
--- a/chrome/test/base/testing_profile_manager.cc
+++ b/chrome/test/base/testing_profile_manager.cc
@@ -130,7 +130,7 @@ TestingProfile* TestingProfileManager::CreateGuestProfile() {
   TestingProfile::Builder().BuildIncognito(profile);
 
   profile_manager_->AddProfile(profile);  // Takes ownership.
-  profile_manager_->SetGuestProfilePrefs(profile);
+  profile_manager_->SetNonPersonalProfilePrefs(profile);
 
   testing_profiles_.insert(std::make_pair(kGuestProfileName, profile));