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
IPreferenceStore store= getPreferenceStore();
		return store.getBoolean(OVERVIEW_RULER);
	}
	
	private Color getColor(String key) {
		RGB rgb= PreferenceConverter.getColor(getPreferenceStore(), key);
		return getColor(rgb);
	}
	
	private Color getColor(RGB rgb) {
		JavaTextTools textTools= JavaPlugin.getDefault().getJavaTextTools();
		return textTools.getColorManager().getColor(rgb);
	}
	
	private Color getColor(AnnotationType annotationType) {
		AnnotationInfo info= (AnnotationInfo) ANNOTATION_MAP.get(annotationType);
		if (info != null)
			return getColor(info.fColorPreference);
		return null;
	}
	
	/*
	 * @see AbstractTextEditor#dispose()
	 */
	public void dispose() {
		ISourceViewer sourceViewer= getSourceViewer();
		if (sourceViewer instanceof ITextViewerExtension)
			((ITextViewerExtension) sourceViewer).removeVerifyKeyListener(fBracketInserter);
		if (fPropertyChangeListener != null) {
			Preferences preferences= JavaCore.getPlugin().getPluginPreferences();