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
if (fTabRatio == 0)
				return 0;
				
			int remainder= offsetInLine % fTabRatio;
			remainder= fTabRatio - remainder;
			for (int i= 0; i < remainder; i++)
				buffer.append(' ');
			return remainder;
		}
		
		public void customizeDocumentCommand(IDocument document, DocumentCommand command) {
			String text= command.text;
			if (text == null)
				return;
				
			int index= text.indexOf('\t');
			if (index > -1) {
				
				StringBuffer buffer= new StringBuffer();
				
				fLineTracker.set(command.text);
				int lines= fLineTracker.getNumberOfLines();
				
				try {
						
						for (int i= 0; i < lines; i++) {
							
							int offset= fLineTracker.getLineOffset(i);
							int endOffset= offset + fLineTracker.getLineLength(i);