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 (nextErrorPosition != null) {
			errorPosition.setOffset(nextErrorPosition.getOffset());
			errorPosition.setLength(nextErrorPosition.getLength());
		}
		
		return nextError;
	}
	
	/*
	 * @see AbstractTextEditor#isSaveAsAllowed() 
	 */
	public boolean isSaveAsAllowed() {
		return true;
	}
	
	/**
	 * The compilation unit editor implementation of this  <code>AbstractTextEditor</code>
	 * method asks the user for the workspace path of a file resource and saves the document
	 * there. See http://dev.eclipse.org/bugs/show_bug.cgi?id=6295
	 */
	protected void performSaveAs(IProgressMonitor progressMonitor) {
		
		Shell shell= getSite().getShell();
		IEditorInput input = getEditorInput();
		
		SaveAsDialog dialog= new SaveAsDialog(shell);
		
		IFile original= (input instanceof IFileEditorInput) ? ((IFileEditorInput) input).getFile() : null;
		if (original != null)
			dialog.setOriginalFile(original);