public void setViewer(FrameDiffTool.DiffViewer viewer) {
    ThreadingAssertions.assertEventDispatchThread();

    if (viewer instanceof UnifiedDiffViewer) {
      myCaretTracker = new UnifiedCaretTracker((UnifiedDiffViewer)viewer);
    }
    else if (viewer instanceof SimpleDiffViewer) {
      myCaretTracker = new SimpleCaretTracker((SimpleDiffViewer)viewer);
    }
    else {
      myCaretTracker = null;
    }
  }
public void setViewer(FrameDiffTool.DiffViewer viewer)