Implement CSS parser part for ::slotted pseudo element

third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp

Index: third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp b/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
index 397db5b47fab88bc1d0e205023d0501ffaa2033b..4e2f8bd9d9600cbac80259571414731a9a5e130b 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
@@ -23,6 +23,9 @@ static void recordSelectorStats(const CSSParserContext& context, const CSSSelect
             case CSSSelector::PseudoUnresolved:
                 feature = UseCounter::CSSSelectorPseudoUnresolved;
                 break;
+            case CSSSelector::PseudoSlotted:
+                feature = UseCounter::CSSSelectorPseudoSlotted;
+                break;
             case CSSSelector::PseudoContent:
                 feature = UseCounter::CSSSelectorPseudoContent;
                 break;
@@ -384,6 +387,19 @@ PassOwnPtr<CSSParserSelector> CSSSelectorParser::consumePseudo(CSSParserTokenRan
             selector->adoptSelectorVector(selectorVector);
             return selector.release();
         }
+    case CSSSelector::PseudoSlotted:
+        {
+            DisallowPseudoElementsScope scope(this);
+
+            OwnPtr<CSSParserSelector> innerSelector = consumeCompoundSelector(block);
+            block.consumeWhitespace();
+            if (!innerSelector || !block.atEnd() || !RuntimeEnabledFeatures::shadowDOMV1Enabled())
+                return nullptr;
+            Vector<OwnPtr<CSSParserSelector>> selectorVector;
+            selectorVector.append(innerSelector.release());
+            selector->adoptSelectorVector(selectorVector);
+            return selector.release();
+        }
     case CSSSelector::PseudoLang:
         {
             // FIXME: CSS Selectors Level 4 allows :lang(*-foo)
@@ -620,7 +636,11 @@ PassOwnPtr<CSSParserSelector> CSSSelectorParser::splitCompoundAtImplicitShadowCr
     // the selector parser as a single compound selector.
     //
     // Example: input#x::-webkit-clear-button -> [ ::-webkit-clear-button, input, #x ]
-
+    //
+    // Likewise, ::slotted() pseudo element has an implicit ShadowSlot combinator to its left
+    // for finding matching slot element in other TreeScope.
+    //
+    // Example: slot[name=foo]::slotted(div) -> [ div, slot, [name=foo] ]
     CSSParserSelector* splitAfter = compoundSelector.get();
 
     while (splitAfter->tagHistory() && !splitAfter->tagHistory()->needsImplicitShadowCrossingCombinatorForMatching())
@@ -630,7 +650,7 @@ PassOwnPtr<CSSParserSelector> CSSSelectorParser::splitCompoundAtImplicitShadowCr
         return compoundSelector;
 
     OwnPtr<CSSParserSelector> secondCompound = splitAfter->releaseTagHistory();
-    secondCompound->appendTagHistory(CSSSelector::ShadowPseudo, compoundSelector);
+    secondCompound->appendTagHistory(secondCompound->pseudoType() == CSSSelector::PseudoSlotted ? CSSSelector::ShadowSlot : CSSSelector::ShadowPseudo, compoundSelector);
     return secondCompound.release();
 }