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
* current caret location are automatically marked in
	 * this editor.
	 * @since 3.0
	 */
	private boolean fMarkOccurrenceAnnotations;
	/**
	 * Tells whether the occurrence annotations are sticky
	 * i.e. whether they stay even if there's no valid Java
	 * element at the current caret position.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fStickyOccurrenceAnnotations;
	/**
	 * Tells whether to mark type occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkTypeOccurrences;
	/**
	 * Tells whether to mark method occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */
	private boolean fMarkMethodOccurrences;
	/**
	 * Tells whether to mark constant occurrences in this editor.
	 * Only valid if {@link #fMarkOccurrenceAnnotations} is <code>true</code>.
	 * @since 3.0
	 */