Allow HTMLPlugInElement to host UA shadow DOM.

Source/core/html/HTMLAppletElement.cpp

Index: Source/core/html/HTMLAppletElement.cpp
diff --git a/Source/core/html/HTMLAppletElement.cpp b/Source/core/html/HTMLAppletElement.cpp
index 8411681649e60e12d2bd27046daff47d4b798194..d67f502d0096f10ea88ab65834b0ee8d604ddf57 100644
--- a/Source/core/html/HTMLAppletElement.cpp
+++ b/Source/core/html/HTMLAppletElement.cpp
@@ -34,6 +34,7 @@
 #include "core/frame/Settings.h"
 #include "core/frame/csp/ContentSecurityPolicy.h"
 #include "core/rendering/RenderApplet.h"
+#include "core/rendering/RenderBlockFlow.h"
 #include "platform/Widget.h"
 #include "platform/weborigin/KURL.h"
 #include "platform/weborigin/SecurityOrigin.h"
@@ -95,6 +96,9 @@ RenderObject* HTMLAppletElement::createRenderer(RenderStyle* style)
     if (!canEmbedJava() || hasAuthorShadowRoot())
         return RenderObject::createObject(this, style);
 
+    if (usePlaceholderContent())
+        return new RenderBlockFlow(this);
+
     return new RenderApplet(this);
 }