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
if (astRoot == null || selection == null)
			return;
		
		IDocument document= getSourceViewer().getDocument();
		if (document == null)
			return;
		
		List matches= null;
		if (fMarkExceptions || fMarkTypeOccurrences) {
			ExceptionOccurrencesFinder exceptionFinder= new ExceptionOccurrencesFinder();
			String message= exceptionFinder.initialize(astRoot, selection.getOffset(), selection.getLength());
			if (message == null) {
				matches= exceptionFinder.perform();
				if (!fMarkExceptions && !matches.isEmpty())
					matches.clear();
			}
		}
		
		if ((matches == null || matches.isEmpty()) && (fMarkMethodExitPoints || fMarkTypeOccurrences)) {
			MethodExitsFinder finder= new MethodExitsFinder();
			String message= finder.initialize(astRoot, selection.getOffset(), selection.getLength());
			if (message == null) {
				matches= finder.perform();
				if (!fMarkMethodExitPoints && !matches.isEmpty())
					matches.clear();
			}
		}
		
		if ((matches == null || matches.isEmpty()) && (fMarkImplementors || fMarkTypeOccurrences)) {