Bug 17699 Java Editor: Local Histroy menu entries are enabled for read-only files
F1 - make file read-only - open it - observe: context menu contains Local History actions. Only compare makes sense for read-only files
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/compare/JavaHistoryAction.java
/**
	 * Implements the IStreamContentAccessor and ITypedElement protocols
	 * for a TextBuffer.
	 */
	class JavaTextBufferNode implements ITypedElement, IStreamContentAccessor {