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
* Informs the editor that its outliner has been closed.
	 */
	public void outlinePageClosed() {
		if (fOutlinePage != null) {
			fOutlineSelectionChangedListener.uninstall(fOutlinePage);
			fOutlinePage= null;
			resetHighlightRange();
		}
	}
	/**
	 * Synchronizes the outliner selection with the given element
	 * position in the editor.
	 * 
	 * @param element the java element to select
	 */
	protected void synchronizeOutlinePage(ISourceReference element) {
		synchronizeOutlinePage(element, true);
	}
	
	/**
	 * Synchronizes the outliner selection with the given element
	 * position in the editor.
	 * 
	 * @param element the java element to select
	 * @param checkIfOutlinePageActive <code>true</code> if check for active outline page needs to be done
	 */
	protected void synchronizeOutlinePage(ISourceReference element, boolean checkIfOutlinePageActive) {
		if (fOutlinePage != null && element != null && !(checkIfOutlinePageActive && isJavaOutlinePageActive())) {
			fOutlineSelectionChangedListener.uninstall(fOutlinePage);
			fOutlinePage.select(element);