servo: Merge #10208 - Generate html and json of supported css properties (from jrasanen:jr/issue10196); r=SimonSapin

Fixes #10196. Outputs html and json of supported css properties to `target/doc/` directory when deploying github-pages.

Source-Repo: https://github.com/servo/servo
Source-Revision: df73a18a61e57f62e2e17541d45dcd3818b35b7c

servo/python/servo/testing_commands.py

@@ -163,10 +163,17 @@ class MachCommands(CommandBase):
     @CommandArgument('test_name', nargs=argparse.REMAINDER,
                      help="Only run tests that match this pattern or file path")
     def test_unit(self, test_name=None, package=None):
-        properties = json.loads(subprocess.check_output([
+        subprocess.check_output([
             sys.executable,
             path.join(self.context.topdir, "components", "style", "list_properties.py")
-        ]))
+        ])
+
+        this_file = os.path.dirname(__file__)
+        servo_doc_path = os.path.abspath(os.path.join(this_file, '../', '../', 'target', 'doc', 'servo'))
+
+        with open(os.path.join(servo_doc_path, 'css-properties.json'), 'r') as property_file:
+            properties = json.loads(property_file.read())
+
         assert len(properties) >= 100
         assert "margin-top" in properties
         assert "margin" in properties