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
/*
		 * @see org.eclipse.jface.action.IAction#run()
		 */
		public void run() {
			final JavaSourceViewer viewer= (JavaSourceViewer) getSourceViewer();
			if (viewer.isEditable()) {
				final Point selection= viewer.rememberSelection();
				try {
					viewer.setRedraw(false);
					final String type= TextUtilities.getContentType(viewer.getDocument(), IJavaPartitions.JAVA_PARTITIONING, selection.x, true);
					if (type.equals(IDocument.DEFAULT_CONTENT_TYPE) && selection.y == 0) {
						try {
							final IJavaElement element= getElementAt(selection.x, true);
							if (element != null && element.exists()) {
								final int kind= element.getElementType();
								if (kind == IJavaElement.TYPE || kind == IJavaElement.METHOD || kind == IJavaElement.INITIALIZER) {
									final ISourceReference reference= (ISourceReference)element;
									final ISourceRange range= reference.getSourceRange();
									if (range != null) {
										viewer.setSelectedRange(range.getOffset(), range.getLength());
										viewer.doOperation(ISourceViewer.FORMAT);
									}
								}
							}
						} catch (JavaModelException exception) {