Auto merge of #17260 - jyc:CSSStyleRule-style-test, r=jdm,emilio

Correctly test CSSStyleRule.style.

<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

- [X] These changes do not require tests

This is part of a series of PRs to fix https://github.com/servo/servo/issues/17182

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tests/wpt/metadata/MANIFEST.json

@@ -553854,7 +553854,7 @@
    "testharness"
   ],
   "cssom/CSSStyleRule.html": [
-   "b7cfe3da8454d5c64a25c440e0776c80d8c3a751",
+   "83a876458ba609b81c86354160549ab11b018d38",
    "testharness"
   ],
   "cssom/CSSStyleSheet.html": [

tests/wpt/metadata/cssom/CSSStyleRule.html.ini

@@ -9,9 +9,9 @@
   [Values of CSSRule attributes]
     expected: FAIL
 
-  [Existence, writability and type of CSSStyleRule attributes]
-    expected: FAIL
-
   [Values of CSSStyleRule attributes]
     expected: FAIL
 
+  [Existence and type of CSSStyleRule attributes]
+    expected: FAIL
+

tests/wpt/web-platform-tests/cssom/CSSStyleRule.html

@@ -67,8 +67,24 @@
             assert_idl_attribute(rule, "selectorText");
             assert_equals(typeof rule.selectorText, "string");
             assert_idl_attribute(rule, "style");
-            assert_readonly(rule, "style");
-        }, "Existence, writability and type of CSSStyleRule attributes");
+        }, "Existence and type of CSSStyleRule attributes");
+
+        test(function() {
+            // CSSStyleRule.style has PutForwards=cssText and SameObject.
+            var initial = rule.style.cssText;
+            var style = rule.style;
+
+            rule.style = "";
+            assert_equals(rule.style.cssText, "");
+            assert_equals(rule.style, style);
+
+            rule.style = "margin: 42px;";
+            assert_equals(rule.style.margin, "42px");
+            assert_equals(rule.style, style);
+
+            rule.style = initial;
+            assert_equals(rule.style, style);
+        }, "Assigning to CSSStyleRule.style assigns to cssText; CSSStyleRule.style returns the same object");
 
         test(function() {
             assert_equals(rule.selectorText, "div");