Reland r165040 "Make ancestors of modal <dialog> inert"

Source/core/dom/Node.cpp

Index: Source/core/dom/Node.cpp
diff --git a/Source/core/dom/Node.cpp b/Source/core/dom/Node.cpp
index 2c1dc4c1baf841dd990e8fe7c0838f2d70b72a92..5e1deff6b7f1d6b202f20602df3b04450f146514 100644
--- a/Source/core/dom/Node.cpp
+++ b/Source/core/dom/Node.cpp
@@ -792,7 +792,7 @@ bool Node::shouldHaveFocusAppearance() const
 bool Node::isInert() const
 {
     const HTMLDialogElement* dialog = document().activeModalDialog();
-    if (dialog && !containsIncludingShadowDOM(dialog) && !dialog->containsIncludingShadowDOM(this))
+    if (dialog && this != document() && !dialog->containsIncludingShadowDOM(this))
         return true;
     return document().ownerElement() && document().ownerElement()->isInert();
 }