Update the behavior of ShadowRoot.activeElement to match the latest spec

third_party/WebKit/Source/core/dom/TreeScope.cpp

Index: third_party/WebKit/Source/core/dom/TreeScope.cpp
diff --git a/third_party/WebKit/Source/core/dom/TreeScope.cpp b/third_party/WebKit/Source/core/dom/TreeScope.cpp
index b7b72b8f4f9f5b7eefbd57ba33144125439dc7a5..64707e75a5b5a26443738d5c541f20682e1d6e10 100644
--- a/third_party/WebKit/Source/core/dom/TreeScope.cpp
+++ b/third_party/WebKit/Source/core/dom/TreeScope.cpp
@@ -429,6 +429,14 @@ Element* TreeScope::adjustedFocusedElement() const
     if (!element)
         return nullptr;
 
+    if (rootNode().isInV1ShadowTree()) {
+        if (Node* retargeted = rootNode().retarget(*element)) {
+            DCHECK(retargeted->isElementNode());
+            return this == &retargeted->treeScope() ? toElement(retargeted) : nullptr;
+        }
+        return nullptr;
+    }
+
     RawPtr<EventPath> eventPath = new EventPath(*element);
     for (size_t i = 0; i < eventPath->size(); ++i) {
         if (eventPath->at(i).node() == rootNode()) {