wpt: Update some security-features scripts to run under Python 3.

In Python 3, dict.keys() returns an object which doesn't have
a remove() method. Instead, this is converted to a list so that
this kind of manipulation is possible.

basestring no longer exists in Python 3, so str is used instead.
Technically basestring also includes bytes, but as far as I can
tell it's not reasonable for bytes to end up here.

Finally, message is not guaranteed to exist, so the error object
itself is printed instead.

Change-Id: Iad38779f8cfcfe1f464b73e8cbabef923d90f6ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5090427
Reviewed-by: Hiroshige Hayashizaki <[email protected]>
Commit-Queue: Jeremy Roman <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1234071}

common/security-features/tools/generate.py

@@ -321,7 +321,7 @@ def generate_test_source_files(spec_directory, test_helper_filenames,
     # Choose a debug/release template depending on the target.
     html_template = "test.%s.html.template" % target
 
-    artifact_order = test_expansion_schema.keys()
+    artifact_order = list(test_expansion_schema.keys())
     artifact_order.remove('expansion')
 
     excluded_selection_pattern = ''

common/security-features/tools/spec_validator.py

@@ -5,7 +5,7 @@
 
 def assert_non_empty_string(obj, field):
     assert field in obj, 'Missing field "%s"' % field
-    assert isinstance(obj[field], basestring), \
+    assert isinstance(obj[field], str), \
         'Field "%s" must be a string' % field
     assert len(obj[field]) > 0, 'Field "%s" must not be empty' % field
 
@@ -34,7 +34,7 @@ def assert_value_from(obj, field, items):
 
 
 def assert_atom_or_list_items_from(obj, field, items):
-    if isinstance(obj[field], basestring) or isinstance(
+    if isinstance(obj[field], str) or isinstance(
             obj[field], int) or obj[field] is None:
         assert_value_from(obj, field, items)
         return
@@ -236,7 +236,7 @@ def assert_valid_spec_json(spec_json):
     try:
         validate(spec_json, error_details)
     except AssertionError as err:
-        print('ERROR:', err.message)
+        print('ERROR:', err)
         print(json.dumps(error_details, indent=4))
         sys.exit(1)