Do bloom filter rejection for ::slotted selectors

After we started doing style recalc in flat tree order, disabling fast
rejection for ::slotted should not be necessary.

Bug: 1159206
Change-Id: I746eefa85aaaa2d53ec80de5c837a55fa0e108e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2596296
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838009}

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

@@ -169,9 +169,6 @@ void SelectorFilter::CollectIdentifierHashes(
         skip_over_subselectors = true;
         break;
       case CSSSelector::kShadowSlot:
-        // Disable fastRejectSelector.
-        *identifier_hashes = 0;
-        return;
       case CSSSelector::kDescendant:
       case CSSSelector::kChild:
       case CSSSelector::kUAShadow:

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

@@ -3877,4 +3877,45 @@ TEST_F(StyleEngineTest, FastRejectForHostChild) {
   EXPECT_EQ(1u, stats->rules_fast_rejected);
 }
 
+TEST_F(StyleEngineTest, RejectSlottedSelector) {
+  GetDocument().body()->setInnerHTML(R"HTML(
+    <div id="host">
+      <span id="slotted"></span>
+    </div>
+  )HTML");
+
+  Element* host = GetDocument().getElementById("host");
+  ASSERT_TRUE(host);
+  ShadowRoot& shadow_root =
+      host->AttachShadowRootInternal(ShadowRootType::kOpen);
+  shadow_root.setInnerHTML(R"HTML(
+    <style>
+      .notfound ::slotted(span) {
+        color: pink;
+      }
+    </style>
+    <slot></slot>
+  )HTML");
+  UpdateAllLifecyclePhases();
+
+  StyleEngine& engine = GetStyleEngine();
+  // If the Stats() were already enabled, we would not start with 0 counts.
+  EXPECT_FALSE(engine.Stats());
+  engine.SetStatsEnabled(true);
+
+  StyleResolverStats* stats = engine.Stats();
+  ASSERT_TRUE(stats);
+  EXPECT_EQ(0u, stats->rules_fast_rejected);
+
+  Element* span = GetDocument().getElementById("slotted");
+  ASSERT_TRUE(span);
+  span->SetInlineStyleProperty(CSSPropertyID::kColor, "green");
+
+  GetDocument().Lifecycle().AdvanceTo(DocumentLifecycle::kInStyleRecalc);
+  GetStyleEngine().RecalcStyle();
+
+  // Should fast reject ".notfound ::slotted(span)"
+  EXPECT_EQ(1u, stats->rules_fast_rejected);
+}
+
 }  // namespace blink