After locking a profile and showing the User Manager, make Guest the active profile

chrome/browser/profiles/profiles_state.h

Index: chrome/browser/profiles/profiles_state.h
diff --git a/chrome/browser/profiles/profiles_state.h b/chrome/browser/profiles/profiles_state.h
index 39aae3dafd1cf9fe98f3d939c46391df649b5e08..9abdc0393a8e3c3fc8172254d57c04c286d52649 100644
--- a/chrome/browser/profiles/profiles_state.h
+++ b/chrome/browser/profiles/profiles_state.h
@@ -68,6 +68,11 @@ void UpdateGaiaProfilePhotoIfNeeded(Profile* profile);
 // NULL.
 SigninErrorController* GetSigninErrorController(Profile* profile);
 
+// If the current active profile (given by prefs::kProfileLastUsed) is locked,
+// changes the active profile to the Guest profile and returns it, otherwise
+// returns NULL. This assumes that the Guest profile has been loaded.
+Profile* SetActiveProfileToGuestIfLocked();
+
 }  // namespace profiles
 
 #endif  // CHROME_BROWSER_PROFILES_PROFILES_STATE_H_