void InitTracker ()
{
//if there's a CSharpTextEditorIndentation in the extension chain, we can reuse its stateTracker
CSharpTextEditorIndentation c = this.Document.GetContent<CSharpTextEditorIndentation> ();
if (c != null && c.StateTracker != null) {
stateTracker = c.StateTracker;
} else {
stateTracker = new DocumentStateTracker<CSharpIndentEngine> (new CSharpIndentEngine (policy), textEditorData);
}
}