Add mini_installer not-in-use update test.

chrome/test/mini_installer/test_installer.py

Index: chrome/test/mini_installer/test_installer.py
diff --git a/chrome/test/mini_installer/test_installer.py b/chrome/test/mini_installer/test_installer.py
index 723459b28a9d3e00dd1eaa4d6d91c62a03950127..0f6591c357d1d35e900a08c940206727e2562844 100644
--- a/chrome/test/mini_installer/test_installer.py
+++ b/chrome/test/mini_installer/test_installer.py
@@ -344,12 +344,18 @@ def main():
   assert os.path.exists(mini_installer_path), ('Could not find file %s' %
                                                mini_installer_path)
 
+  next_version_mini_installer_path = os.path.join(
+      args.build_dir, args.target, 'next_version_mini_installer.exe')
+  assert os.path.exists(next_version_mini_installer_path), (
+      'Could not find file %s' % next_version_mini_installer_path)
+
   suite = unittest.TestSuite()
 
   # Set the env var used by mini_installer.exe to decide to not show UI.
   os.environ['MINI_INSTALLER_TEST'] = '1'
 
-  variable_expander = VariableExpander(mini_installer_path)
+  variable_expander = VariableExpander(mini_installer_path,
+                                       next_version_mini_installer_path)
   config = ParseConfigFile(args.config, variable_expander)
 
   RunCleanCommand(args.force_clean, variable_expander)