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 DefaultEncodingSupport fEncodingSupport;
	
	private InformationPresenter fInformationPresenter;
	
	private SelectionHistory fSelectionHistory;
	/**
	 * Indicates whether this editor is about to update any annotation views.
	 * @since 3.0
	 */
	private boolean fIsUpdatingAnnotationViews= false;
	/**
	 * The marker that served as last target for a goto marker request.
	 * @since 3.0
	 */
	private IMarker fLastMarkerTarget= null;
	protected CompositeActionGroup fActionGroups;
	/**
	 * The action group for folding.
	 *  
	 * @since 3.0
	 */
	private FoldingActionGroup fFoldingGroup;
	private CompositeActionGroup fContextMenuGroup;
	/**
	 * Holds the current occurrence annotations.
	 * @since 3.0
	 */
	private Annotation[] fOccurrenceAnnotations= null;
	/**
	 * Tells whether all occurrences of the element at the