Make `mojo_test` run dart apptests in strict mode by default.

mojo/devtools/common/mojo_test

 #!/usr/bin/env python
 # 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.
 
 """Test runner for Mojo application tests.
 
 TODO(vtl|msw): Add a way of specifying data dependencies.
 """
 
@@ skipping 21 matching lines @@
    #   * "gtest_isolated": like "gtest", but run with fixture isolation,
    #      i.e., each test in a fresh mojo_shell
    #   * "dart"
    "type": "gtest",
    # Optional arguments to be passed to the apptest.
    "test-args": ["--an_arg", "another_arg"],
    # Optional shell arguments.
    "shell-args": ["--some-flag-for-the-shell", "--another-flag"],
    # Optional timeout in seconds, 60 by default.
    "timeout": 120,
+   # Optional override for dart content handler strict mode (on by default).
+   "dart_strict_mode": False,
  }
 
 |test_list_file| may reference the |target_os| global that will be any of
 ['android', 'linux'], indicating the system on which the tests are to be run.
 
 Any arguments not recognized by the script will be passed on as shell arguments.
 """
 
 _logger = logging.getLogger()
 
 _CACHE_SERVICE_URL = 'mojo:url_response_disk_cache'
 _NETWORK_SERVICE_URL = 'mojo:network_service'
+_DART_STRICT_MODE_ARG = ('--args-for=mojo:dart_content_handler '
+                         '--enable-strict-mode')
 
 
 def main():
   parser = argparse.ArgumentParser(
       formatter_class=argparse.RawDescriptionHelpFormatter,
       description=_DESCRIPTION)
   parser.add_argument("test_list_file", type=file,
                       help="a file listing apptests to run")
   shell_config.add_shell_arguments(parser)
 
@@ skipping 17 matching lines @@
   test_list = test_list_globals["tests"]
 
   succeeded = True
   for test_dict in test_list:
     test = test_dict["test"]
     test_name = test_dict.get("name", test)
     test_type = test_dict.get("type", "gtest")
     test_args = test_dict.get("test-args", [])
     shell_args = test_dict.get("shell-args", []) + common_shell_args
     timeout = test_dict.get("timeout", 60)
+    dart_strict_mode = test_dict.get("dart_strict_mode", True)
+    if dart_strict_mode:
+      shell_args.append(_DART_STRICT_MODE_ARG)
 
     _logger.info("Will start: %s" % test_name)
     print "Running %s...." % test_name,
     sys.stdout.flush()
 
     if test_type == "dart":
       apptest_result = apptest_dart.run_dart_apptest(shell, shell_args, test,
                                                      test_args, timeout)
     elif test_type == "gtest":
       apptest_result = apptest_gtest.run_gtest_apptest(shell, shell_args, test,
                                                        test_args, timeout,
                                                        False)
     elif test_type == "gtest_isolated":
       apptest_result = apptest_gtest.run_gtest_apptest(shell, shell_args, test,
                                                        test_args, timeout,
                                                        True)
     else:
       apptest_result = False
       print "Unrecognized test type in %r" % test_dict
 
     print "Succeeded" if apptest_result else "Failed"
     _logger.info("Completed: %s" % test_name)
     if not apptest_result:
       succeeded = False
   return 0 if succeeded else 1
 
 if __name__ == '__main__':
   sys.exit(main())