Mark host for style recalc (and child recalc) whenever adding a ShadowRoot

Source/core/dom/shadow/ElementShadow.cpp

Index: Source/core/dom/shadow/ElementShadow.cpp
diff --git a/Source/core/dom/shadow/ElementShadow.cpp b/Source/core/dom/shadow/ElementShadow.cpp
index a11b94627e18f0af0578138171da152443bcc9fb..78c619d2d0bc87ea53f2bae4af4098b124a9e138 100644
--- a/Source/core/dom/shadow/ElementShadow.cpp
+++ b/Source/core/dom/shadow/ElementShadow.cpp
@@ -169,6 +169,9 @@ ShadowRoot& ElementShadow::addShadowRoot(Element& shadowHost, ShadowRoot::Shadow
     setNeedsDistributionRecalc();
 
     shadowRoot->insertedInto(&shadowHost);
+    shadowHost.setChildNeedsStyleRecalc();
+    shadowHost.setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::Shadow));
+
     InspectorInstrumentation::didPushShadowRoot(&shadowHost, shadowRoot.get());
 
     return *shadowRoot;