Add support for new CSS ::slotted() pseudo element

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

Index: third_party/WebKit/Source/core/css/RuleFeature.cpp
diff --git a/third_party/WebKit/Source/core/css/RuleFeature.cpp b/third_party/WebKit/Source/core/css/RuleFeature.cpp
index d1239bc05689afba633b8794f131ad4849309a7f..72ba79dc470cf29e66cb323ed0ac51426c95cb52 100644
--- a/third_party/WebKit/Source/core/css/RuleFeature.cpp
+++ b/third_party/WebKit/Source/core/css/RuleFeature.cpp
@@ -174,7 +174,8 @@ bool supportsInvalidationWithSelectorList(CSSSelector::PseudoType pseudo)
         || pseudo == CSSSelector::PseudoCue
         || pseudo == CSSSelector::PseudoHost
         || pseudo == CSSSelector::PseudoHostContext
-        || pseudo == CSSSelector::PseudoNot;
+        || pseudo == CSSSelector::PseudoNot
+        || pseudo == CSSSelector::PseudoSlotted;
 }
 
 #endif // ENABLE(ASSERT)
@@ -195,6 +196,7 @@ bool requiresSubtreeInvalidation(const CSSSelector& selector)
     case CSSSelector::PseudoHostContext:
         // :host-context matches a shadow host, yet the simple selectors inside
         // :host-context matches an ancestor of the shadow host.
+    case CSSSelector::PseudoSlotted:

[rune, 2015/12/22 14:56:53]

This recalculates a bit more than necessary. Should be possible to do like we do
for ::content where we SubtreeStyleChange insertion points (<content> elements)
which recalculates distributed nodes with descendants.

         return true;
     default:
         ASSERT(supportsInvalidation(selector.pseudoType()));