Clear undo stack when text control is set programatically

Source/core/editing/Editor.cpp

Index: Source/core/editing/Editor.cpp
diff --git a/Source/core/editing/Editor.cpp b/Source/core/editing/Editor.cpp
index ba4484d2aac3492583c216773431702b3b8b7d96..6cb7b61b0bc469897fbc8366c4e3465159f0da3a 100644
--- a/Source/core/editing/Editor.cpp
+++ b/Source/core/editing/Editor.cpp
@@ -953,6 +953,12 @@ void Editor::redo()
         undoStack->redo();
 }
 
+void Editor::clearUndoStack()
+{
+    if (UndoStack* undoStack = this->undoStack())
+        undoStack->clear();
+}
+
 void Editor::setBaseWritingDirection(WritingDirection direction)
 {
     Node* focusedElement = frame().document()->focusedElement();