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

chrome/test/base/testing_profile.h

Index: chrome/test/base/testing_profile.h
diff --git a/chrome/test/base/testing_profile.h b/chrome/test/base/testing_profile.h
index 706072b3093e35dce0fbe156c3017b28182e851e..750ee92d1f176f2bc22f31fcacdd7984d0011e7b 100644
--- a/chrome/test/base/testing_profile.h
+++ b/chrome/test/base/testing_profile.h
@@ -46,6 +46,14 @@ class TestingPrefService;
 
 class TestingProfile : public Profile {
  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 |kInitialProfile|, which is
+  // always "Default", because they are runnining without logged-in user.
+  static const char kTestUserProfileDir[];
+
   // Default constructor that cannot be used with multi-profiles.
   TestingProfile();