Auto merge of #17055 - bzbarsky:sharing-across-ids, r=emilio

Allow style sharing for elements with ids as long as the ID is not being used for styling

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---
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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 part of the problem we're seeing in https://bugzilla.mozilla.org/show_bug.cgi?id=1367862

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because the only impact is on performance and memory.

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tests/unit/style/stylist.rs

@@ -77,11 +77,19 @@ fn test_revalidation_selectors() {
     let test = parse_selectors(&[
         // Not revalidation selectors.
         "div",
-        "#bar",
         "div:not(.foo)",
         "div span",
         "div > span",
 
+        // ID selectors.
+        "#foo1", // FIXME(bz) This one should not be a revalidation
+                // selector once we fix
+                // https://bugzilla.mozilla.org/show_bug.cgi?id=1369611
+        "#foo2::before",
+        "#foo3 > span",
+        "#foo1 > span", // FIXME(bz) This one should not be a
+                        // revalidation selector either.
+
         // Attribute selectors.
         "div[foo]",
         "div:not([foo])",
@@ -122,6 +130,12 @@ fn test_revalidation_selectors() {
       .collect::<Vec<_>>();
 
     let reference = parse_selectors(&[
+        // ID selectors.
+        "#foo1",
+        "#foo2::before",
+        "#foo3 > span",
+        "#foo1 > span",
+
         // Attribute selectors.
         "div[foo]",
         "div:not([foo])",