Lazily generate HistoryItem's serialized form state

Source/core/testing/Internals.cpp

Index: Source/core/testing/Internals.cpp
diff --git a/Source/core/testing/Internals.cpp b/Source/core/testing/Internals.cpp
index 9deea7376d457a6166ae539f223d096a702cc7e6..e21dde42bad0d5c76827adbe32bfa4ee358764dd 100644
--- a/Source/core/testing/Internals.cpp
+++ b/Source/core/testing/Internals.cpp
@@ -721,6 +721,7 @@ void Internals::setFormControlStateOfHistoryItem(const Vector<String>& state, Ex
         exceptionState.throwDOMException(InvalidAccessError, "No history item is available.");
         return;
     }
+    mainItem->clearDocumentState();
     mainItem->setDocumentState(state);
 }
 
@@ -2061,8 +2062,7 @@ PassRefPtrWillBeRawPtr<TypeConversions> Internals::typeConversions() const
 
 Vector<String> Internals::getReferencedFilePaths() const
 {
-    frame()->loader().saveDocumentState();
-    return FormController::getReferencedFilePaths(frame()->loader().currentItem()->documentState());
+    return frame()->loader().currentItem()->getReferencedFilePaths();
 }
 
 void Internals::startTrackingRepaints(Document* document, ExceptionState& exceptionState)