Bug 81983 [preferences] Disabling and enabling folding on small file takes forever
3.1 M4 Using enable/disable folding on a small CU takes forever. This is caused by the recent change to apply the preference to all Java editors. In another (hidden) window (Debug) I had StyledText open which (understandably) took long to react on the preference change. Non-visible editor's should not react to this change until they become visible.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
private boolean fMarkImplementors;
	/**
	 * 
	 */
	private ISelection fForcedMarkOccurrencesSelection;
	/**
	 * The internal shell activation listener for updating occurrences.
	 * @since 3.0
	 */
	private ActivationListener fActivationListener= new ActivationListener();
	private ISelectionListenerWithAST fPostSelectionListenerWithAST;
	private OccurrencesFinderJob fOccurrencesFinderJob;
	
	private OccurrencesFinderJobCanceler fOccurrencesFinderJobCanceler;
	/** 
	 * This editor's projection support 
	 * @since 3.0
	 */
	private ProjectionSupport fProjectionSupport;
	/** 
	 * This editor's projection model updater 
	 * @since 3.0
	 */
	private IJavaFoldingStructureProvider fProjectionModelUpdater;
	/**
	 * The override and implements indicator manager for this editor.
	 * @since 3.0
	 */
	protected OverrideIndicatorManager fOverrideIndicatorManager;
	/**