Allow HTMLPlugInElement to host UA shadow DOM.

Source/core/testing/Internals.h

Index: Source/core/testing/Internals.h
diff --git a/Source/core/testing/Internals.h b/Source/core/testing/Internals.h
index 27f89fa484a30bbb686bb75d6cfc5e778e747e73..5204ba404803039e9d59ab83ec7eb32751902d76 100644
--- a/Source/core/testing/Internals.h
+++ b/Source/core/testing/Internals.h
@@ -54,6 +54,7 @@ class Element;
 class ExceptionState;
 class ExecutionContext;
 class GCObservation;
+class HTMLElement;
 class HTMLMediaElement;
 class InternalProfilers;
 class InternalRuntimeFlags;
@@ -315,6 +316,8 @@ public:
 
     unsigned countHitRegions(CanvasRenderingContext2D*);
 
+    void forcePluginPlaceholder(HTMLElement* plugin, const String& htmlSource, ExceptionState&);
+
 private:
     explicit Internals(Document*);
     Document* contextDocument() const;