Extract `mojo_test` - standalone apptest runner in devtools.

mojo/tools/data/apptests

-# This file contains a list of Mojo gtest unit tests.
-#
-# This must be valid Python. It may use the |config| global that will be a
-# mopy.config.Config object, and must set a |tests| global that will contain the
-# list of tests to run.
-#
-# The entries in |tests| are dictionaries of the form described in
-# devtoolslib/apptest_runner.py.
+# This file contains a list of Mojo apptests. For description of the file
+# format, see `mojo_test` in devtools.
 
 tests = [
   {
     "test": "mojo:asset_bundle_apptests",
   },
   {
     "test": "mojo:authenticating_url_loader_interceptor_apptests",
   },
   {
     "test": "mojo:clipboard_apptests",
@@ skipping 47 matching lines @@
     "shell-args": ["--args-for=mojo:native_viewport_service --use-headless-config --use-osmesa"],
   },
   {
     "test": "mojo:versioning_apptests",
   },
   {
     "test": "mojo:url_response_disk_cache_apptests",
   },
 ]
 
-if config.target_os == config.OS_LINUX:
+if target_os == 'linux':
   tests += [
     {
       "test": "mojo:example_apptests",
       "name": "mojo:example_apptests (python_example_service)",
       # ExampleApplicationTest.CheckCommandLineArg checks --example_apptest_arg.
       "test-args": ["--example_apptest_arg"],
       "shell-args": [
         "--url-mappings=mojo:example_service=mojo:python_example_service"
       ],
     },
     {
       "test": "mojo:mojo_url_redirector_apptests",
       "test-args": ["--redirector_port=49152",
                     "--app_location_files_port=49153"],
       "shell-args": ["--args-for=mojo:mojo_url_redirector 0.0.0.0:49152 http://localhost:49153"],
     }
   ]
 
-if config.target_os == config.OS_ANDROID:
+if target_os == 'android':
   tests += [
     {
       "test": "mojo:example_apptests",
       "name": "mojo:example_apptests (android_example_service)",
       # ExampleApplicationTest.CheckCommandLineArg checks --example_apptest_arg.
       "test-args": ["--example_apptest_arg"],
       "shell-args": [
         "--url-mappings=mojo:example_service=mojo:android_example_service"
       ],
     },
     {
       "test": "mojo:notification_apptests",
     },
     {
       "test": "mojo:shell_nfc_apptests",
     },
   ]
 
-if config.target_os != config.OS_ANDROID:
+if target_os != 'android':
   tests += [
     {
       "test": "mojo:js_apptests",
       "type": "gtest_isolated",
     },
     {
       "test": "mojo:reaper_apptests",
     },
     {
       "test": "mojo:dart_apptests",
       "type": "dart",
     },
     {
       # https://github.com/domokit/mojo/issues/61
       # Sometime the shell get a trucated application when exposed through the
       # http server.
       "test": "mojo:shell_apptests",
     },
   ]