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
/*
		 * @see ISourceViewer#showAnnotations(boolean)
		 */
		public void showAnnotations(boolean show) {
			fCachedIsVerticalRulerVisible= (show && fCachedVerticalRuler != null);
			super.showAnnotations(show);
		}
		
		public IContentAssistant getContentAssistant() {
			return fContentAssistant;
		}
		
		/*
		 * @see ITextOperationTarget#doOperation(int)
		 */
		public void doOperation(int operation) {
		
			if (getTextWidget() == null)
				return;
			
			switch (operation) {
				case CONTENTASSIST_PROPOSALS:
					String msg= fContentAssistant.showPossibleCompletions();
					setStatusLineErrorMessage(msg);
					return;
				case UNDO:
					fIgnoreTextConverters= true;
					break;
				case REDO:
					fIgnoreTextConverters= true;