Auto merge of #16467 - canaltinova:contain, r=emilio

stylo: Add glue for contain property

In gecko, `size` and `content` values aren't implemented yet. So I had to disable these parts with mako. We will need to update the property and the glue once these are implemented in gecko.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1354998](https://bugzilla.mozilla.org/show_bug.cgi?id=1354998)

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tests/unit/style/parsing/containment.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use parsing::parse;
+use style_traits::ToCss;
 
 #[test]
 fn contain_longhand_should_parse_correctly() {
@@ -13,11 +14,14 @@ fn contain_longhand_should_parse_correctly() {
     assert_eq!(none, SpecifiedValue::empty());
 
     let strict = parse_longhand!(contain, "strict");
-    assert_eq!(strict, contain::STRICT);
+    assert_eq!(strict, contain::STRICT | contain::STRICT_BITS);
 
     let style_paint = parse_longhand!(contain, "style paint");
     assert_eq!(style_paint, contain::STYLE | contain::PAINT);
 
+    assert_roundtrip_with_context!(contain::parse, "strict");
+    assert_roundtrip_with_context!(contain::parse, "layout style paint");
+
     // Assert that the `2px` is not consumed, which would trigger parsing failure in real use
     assert_parser_exhausted!(contain::parse, "layout 2px", false);
 }