The User Manager should be backed by a special profile, not the guest one.

chrome/test/base/testing_profile_manager.h

Index: chrome/test/base/testing_profile_manager.h
diff --git a/chrome/test/base/testing_profile_manager.h b/chrome/test/base/testing_profile_manager.h
index b4c1dda39d3197ce30a4a4719699b218f657d498..be7836f4fdb8a7839c6f35fe2639fd794157c758 100644
--- a/chrome/test/base/testing_profile_manager.h
+++ b/chrome/test/base/testing_profile_manager.h
@@ -67,11 +67,18 @@ class TestingProfileManager {
   // The subsystem owns the Profile and returns a weak pointer.
   TestingProfile* CreateGuestProfile();
 
+  // Creates a TestingProfile whose data lives in the User Manager profile
+  // test environment directory, as specified by the profile manager.
+  // This profile will not be added to the ProfileInfoCache. This will
+  // register the TestingProfile with the profile subsystem as well.
+  // The subsystem owns the Profile and returns a weak pointer.
+  TestingProfile* CreateUserManagerProfile();
+
   // Deletes a TestingProfile from the profile subsystem.
   void DeleteTestingProfile(const std::string& profile_name);
 
-  // Deletes a guest TestingProfile from the profile manager.
-  void DeleteGuestProfile();
+  // Deletes a TestingProfile with |path| from the profile subsystem.
+  void DeleteProfileWithPath(const base::FilePath& path);
 
   // Deletes the cache instance. This is useful for testing that the cache is
   // properly persisting data.