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
super.customizeDocumentCommand(command);
			if (!fIgnoreTextConverters && fTextConverters != null) {
				for (Iterator e = fTextConverters.iterator(); e.hasNext();)
					((ITextConverter) e.next()).customizeDocumentCommand(getDocument(), command);
			}
			fIgnoreTextConverters= false;
		}
		
		public IVerticalRuler getVerticalRuler() {
			return fCachedVerticalRuler;
		}
		
		public boolean isVerticalRulerVisible() {
			return fCachedIsVerticalRulerVisible;
		}
		
		public OverviewRuler getOverviewRuler() {
			return fOverviewRuler;
		}
		
		/*
		 * @see TextViewer#createControl(Composite, int)
		 */
		protected void createControl(Composite parent, int styles) {
			
		}
		
		protected void delayedCreateControl(Composite parent, int styles) {
			
			super.createControl(parent, styles);