Bug 28698 Ctrl+O (show outline) does not work if the file being shown in the editor is read only
M4 The summary tells all. Works if the file is not read only. Is this by design?
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitEditor.java
private SelectionHistory fSelectionHistory;
	
	private IPropertyChangeListener fPropertyChangeListener= new PropertyChangeListener();
	
	private IJavaElement fRememberedElement;
	
	private ITextSelection fRememberedSelection;
	
	private int fRememberedElementOffset;
	
	private BracketInserter fBracketInserter= new BracketInserter();
	
	
	private GenerateActionGroup fGenerateActionGroup;
	private CompositeActionGroup fContextMenuGroup;
	
	/**
	 * Creates a new compilation unit editor.
	 */
	public CompilationUnitEditor() {
		super();
		setDocumentProvider(JavaPlugin.getDefault().getCompilationUnitDocumentProvider());
		setEditorContextMenuId("#CompilationUnitEditorContext"); 
		setRulerContextMenuId("#CompilationUnitRulerContext"); 
		setOutlinerContextMenuId("#CompilationUnitOutlinerContext"); 
		
		fSavePolicy= null;
			
		fJavaEditorErrorTickUpdater= new JavaEditorErrorTickUpdater(this);
	}