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 IDocument fDocument;
		private ISelection fSelection;
		private ISelectionValidator fPostSelectionValidator;
		private boolean fCanceled= false;
		private IProgressMonitor fProgressMonitor;
		private Position[] fPositions;
		
		public OccurrencesFinderJob(IDocument document, Position[] positions, ISelection selection) {
			super(JavaEditorMessages.getString("JavaEditor.markOccurrences.job.name")); 
			fDocument= document;
			fSelection= selection;
			fPositions= positions;
			
			if (getSelectionProvider() instanceof ISelectionValidator)
				fPostSelectionValidator= (ISelectionValidator)getSelectionProvider(); 
		}
		
		
		void doCancel() {
			fCanceled= true;
			cancel();