[cros] Fake a stub user login when no --login-manager and --login-user are given.

chrome/browser/profiles/profile_manager.h

Index: chrome/browser/profiles/profile_manager.h
diff --git a/chrome/browser/profiles/profile_manager.h b/chrome/browser/profiles/profile_manager.h
index bcbbfc35266f77b34cc80c044532efa646aeaa68..b7f2747936d6b7ef09b42809663c65561bf0d5b8 100644
--- a/chrome/browser/profiles/profile_manager.h
+++ b/chrome/browser/profiles/profile_manager.h
@@ -36,6 +36,14 @@ class ProfileManager : public base::NonThreadSafe,
                        public content::NotificationObserver,
                        public Profile::Delegate {
  public:
+  // Profile directory name for the test user. This is "Default" on most
+  // platforms but must be different on ChromeOS because a logged-in user cannot
+  // use "Default" as profile directory.
+  // Browser- and UI tests should always use this to get to the user's profile
+  // directory. Unit-tests, though, should use "Default" always because they
+  // are runnining without logged-in user.
+  static const char kTestUserProfile[];
+
   typedef base::Callback<void(Profile*, Profile::CreateStatus)> CreateCallback;
 
   explicit ProfileManager(const FilePath& user_data_dir);