[:is/:where] Add features to nested complex selectors

This adds (basic) support for adding features to nested complex
selectors.

Bug: 568705
Change-Id: I1f0512ac148bc1f5810787e68777b2d14bd94089
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435225
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812275}

third_party/blink/renderer/core/css/rule_feature_set.cc

@@ -874,8 +874,8 @@ void RuleFeatureSet::AddFeaturesToInvalidationSetsForSelectorList(
        sub_selector; sub_selector = CSSSelectorList::Next(*sub_selector)) {
     descendant_features.has_features_for_rule_set_invalidation = false;
 
-    AddFeaturesToInvalidationSetsForCompoundSelector(
-        *sub_selector, sibling_features, descendant_features);
+    AddFeaturesToInvalidationSets(*sub_selector, sibling_features,
+                                  descendant_features);
 
     if (!descendant_features.has_features_for_rule_set_invalidation)
       selector_list_contains_universal = true;

third_party/blink/renderer/core/css/rule_feature_set_test.cc

@@ -1516,6 +1516,14 @@ RefTestData ref_equal_test_data[] = {
     // selector in the ref.
     {".a :is(.b, .c:nth-child(1))",
      ".a .b, .a .c:nth-child(1), .b:nth-child(1)"},
+    {":is(.a) .b", ".a .b"},
+    {":is(.a, .b) .c", ".a .c, .b .c"},
+    {":is(.a .b, .c .d) .e", ".a .b .e, .c .d .e"},
+    {":is(:is(.a .b, .c) :is(.d, .e .f), .g) .h",
+     ".a .b .h, .c .h, .d .h, .e .f .h, .g .h"},
+    {":is(.a, .b) :is(.c, .d)", ".a .c, .a .d, .b .c, .b .d"},
+    {":is(.a .b, .c .d) :is(.e .f, .g .h)",
+     ".a .b .f, .a .b .h, .c .d .f, .c .d .h, .e .f, .g .h"},
     // clang-format on
 };