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
int i= 0;
		for (Iterator each= matches.iterator(); each.hasNext();) {
			ASTNode currentNode= (ASTNode)each.next();
			positions[i++]= new Position(currentNode.getStartPosition(), currentNode.getLength());
		}
		
		fOccurrencesFinderJob= new OccurrencesFinderJob(document, positions, selection);
		
		
		
		fOccurrencesFinderJob.run(new NullProgressMonitor());
	}
	
	protected void installOccurrencesFinder() {
		fMarkOccurrenceAnnotations= true;
		
		fPostSelectionListenerWithAST= new ISelectionListenerWithAST() {
			public void selectionChanged(IEditorPart part, ITextSelection selection, CompilationUnit astRoot) {
				updateOccurrenceAnnotations(selection, astRoot);
			}
		};
		SelectionListenerWithASTManager.getDefault().addListener(this, fPostSelectionListenerWithAST);
		if (getSelectionProvider() != null) {
			fForcedMarkOccurrencesSelection= getSelectionProvider().getSelection();
			SelectionListenerWithASTManager.getDefault().forceSelectionChange(this, (ITextSelection)fForcedMarkOccurrencesSelection);
		}
		
		if (fOccurrencesFinderJobCanceler == null) {
			fOccurrencesFinderJobCanceler= new OccurrencesFinderJobCanceler();
			fOccurrencesFinderJobCanceler.install();