Implement CSS parser part for ::slotted pseudo element

third_party/WebKit/Source/core/css/SelectorChecker.cpp

Index: third_party/WebKit/Source/core/css/SelectorChecker.cpp
diff --git a/third_party/WebKit/Source/core/css/SelectorChecker.cpp b/third_party/WebKit/Source/core/css/SelectorChecker.cpp
index 3b72243fdd7c400765bf48753e575aeafbe5e52d..8ea479ca60ffeb9f5538d69ce7554026302c8527 100644
--- a/third_party/WebKit/Source/core/css/SelectorChecker.cpp
+++ b/third_party/WebKit/Source/core/css/SelectorChecker.cpp
@@ -451,6 +451,9 @@ SelectorChecker::Match SelectorChecker::matchForRelation(const SelectorCheckingC
             }
             return SelectorFailsCompletely;
         }
+    case CSSSelector::ShadowSlot:
+        // TODO(kochi): Add this in later CL.
+        return SelectorFailsCompletely;
 
     case CSSSelector::SubSelector:
         ASSERT_NOT_REACHED();