Simplify mojo_shell since it's now only used for Mandoline.

mojo/tools/gtest.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import logging
 import os
 import re
 import subprocess
 import sys
 
@@ skipping 52 matching lines @@
 
 
 def get_fixtures(mojo_shell, apptest):
   """Returns the "Test.Fixture" list from an apptest using mojo_shell.
 
   Tests are listed by running the given apptest in mojo_shell and passing
   --gtest_list_tests. The output is parsed and reformatted into a list like
   [TestSuite.TestFixture, ... ]
   An empty list is returned on failure, with errors logged.
   """
-  command = [mojo_shell,
-             "--args-for={0} --gtest_list_tests".format(apptest),
-             apptest]
+  command = [mojo_shell, "--gtest_list_tests", apptest]
   try:
     list_output = subprocess.check_output(command, stderr=subprocess.STDOUT)
     _logging.debug("Tests listed:\n%s" % list_output)
     return _gtest_list_tests(list_output)
   except Exception as e:
     print "Failed to get test fixtures:"
     _print_process_error(command, e)
   return []
 
 
@@ skipping 14 matching lines @@
   test_list = []
   for line in output_lines:
     if not line:
       continue
     if line[0] != ' ':
       suite = line.strip()
       continue
     test_list.append(suite + line.strip())
 
   return test_list