Add a basic demo mode browser test.

chrome/browser/chromeos/login/authenticator.h

Index: chrome/browser/chromeos/login/authenticator.h
diff --git a/chrome/browser/chromeos/login/authenticator.h b/chrome/browser/chromeos/login/authenticator.h
index 079fb61e09ce76ee2b36b2a9650cbdce14000564..c12fd7530f92e7dc932a548d0bd207a6469d74a2 100644
--- a/chrome/browser/chromeos/login/authenticator.h
+++ b/chrome/browser/chromeos/login/authenticator.h
@@ -58,9 +58,9 @@ class Authenticator : public base::RefCountedThreadSafe<Authenticator> {
 
   // Initiates login into kiosk mode account identified by |app_user_id|.
   // The |app_user_id| is a generated username for the account.
-  // |force_ephemeral| specifies whether to force the session to be ephemeral.
-  virtual void LoginAsKioskAccount(
-      const std::string& app_user_id, bool force_ephemeral) = 0;
+  // |force_guest| specifies whether to force the session to use a guest mount.

[bartfab (slow), 2014/03/20 13:22:29]

No, the mount is an ephemeral mount. Guest happens to use it. As do public
sessions. As do regular users, if the appropriate policy is set.

[rkc, 2014/03/20 21:45:01]

As explained in the other comment, this is not just an ephemeral mount. This is
specifically a guest mount; which is different from a Kiosk user mounted
ephemeral.

+  virtual void LoginAsKioskAccount(const std::string& app_user_id,
+                                   bool force_guest) = 0;
 
   // Completes retail mode login.
   virtual void OnRetailModeLoginSuccess() = 0;