Add a deprecation message for shadow-piercing descendant combinators and shadow pseudo elements.

Source/core/css/SelectorChecker.cpp

Index: Source/core/css/SelectorChecker.cpp
diff --git a/Source/core/css/SelectorChecker.cpp b/Source/core/css/SelectorChecker.cpp
index 7d05b704e5231a59543b1a704821063e02beb54b..f03f7f6f5a635d7fed15d72ff55390a86396a6a0 100644
--- a/Source/core/css/SelectorChecker.cpp
+++ b/Source/core/css/SelectorChecker.cpp
@@ -398,6 +398,8 @@ SelectorChecker::Match SelectorChecker::matchForRelation(const SelectorCheckingC
 
     case CSSSelector::ShadowPseudo:
         {
+            if (!context.isUARule && context.selector->pseudoType() == CSSSelector::PseudoShadow)
+                UseCounter::countDeprecation(context.element->document(), UseCounter::CSSSelectorPseudoShadow);
             // If we're in the same tree-scope as the scoping element, then following a shadow descendant combinator would escape that and thus the scope.
             if (context.scope && context.scope->shadowHost() && context.scope->shadowHost()->treeScope() == context.element->treeScope())
                 return SelectorFailsCompletely;
@@ -413,6 +415,8 @@ SelectorChecker::Match SelectorChecker::matchForRelation(const SelectorCheckingC
 
     case CSSSelector::ShadowDeep:
         {
+            if (!context.isUARule)
+                UseCounter::countDeprecation(context.element->document(), UseCounter::CSSDeepCombinator);
             if (ShadowRoot* root = context.element->containingShadowRoot()) {
                 if (root->type() == ShadowRoot::UserAgentShadowRoot)
                     return SelectorFailsCompletely;