Fix and cleanup Mojo and Mandoline python scripts.

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 following form:
 #   {
 #     # Required URL for apptest.
 #     "test": "mojo:test_app_url",
 #     # Optional display name (otherwise the entry for "test" above is used).
 #     "name": "mojo:test_app_url (more details)",
 #     # Optional test type. Valid values:
 #     #   * "gtest" (default)
 #     #   * "gtest_isolated": like "gtest", but run with fixture isolation,
 #     #      i.e., each test in a fresh mojo_shell)
-#     #   * "dart".
 #     "type": "gtest",
 #     # Optional arguments for the apptest.
 #     "test-args": ["--an_arg", "another_arg"],
 #     # Optional arguments for the shell.
 #     "shell-args": ["--some-flag-for-the-shell", "--another-flag"],
 #   }
 #
 # TODO(vtl|msw): Add a way of specifying data dependencies.
 
 tests = [
@@ skipping 21 matching lines @@
       "type": "gtest_isolated",
       "shell-args": [
         "--use-headless-config",
         "--url-mappings=mojo:window_manager=mojo:test_window_manager"
       ]
     },
     {
       "test": "mojo:resource_provider_apptests",
     },
   ]