Clear undo stack when text control is set programatically

Source/core/editing/UndoStack.cpp

 /*
  * Copyright (C) 2006, 2007 Apple, Inc.  All rights reserved.
  * Copyright (C) 2012 Google, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 103 matching lines @@
         RefPtr<UndoStep> step(*back);
         m_redoStack.remove(back);
 
         ASSERT(!m_inRedo);
         TemporaryChange<bool> redoScope(m_inRedo, true);
         step->reapply();
         // reapply will call us back to push this command onto the undo stack.
     }
 }
 
+void UndoStack::clear()
+{
+    if (canUndo())

[eseidel, 2014/03/04 02:08:16]

Why check canUndo here?

+        m_undoStack.clear();
+
+    if (canRedo())
+        m_redoStack.clear();
+}
+
 } // namesace WebCore