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
* Semantic highlighting manager
	 * @since 3.0
	 */
	private SemanticHighlightingManager fSemanticManager;
	
	
	/**
	 * Returns the most narrow java element including the given offset.
	 * 
	 * @param offset the offset inside of the requested element
	 * @return the most narrow java element
	 */
	abstract protected IJavaElement getElementAt(int offset);
	
	/**
	 * Returns the java element of this editor's input corresponding to the given IJavaElement.
	 * 
	 * @param element the java element
	 * @return the corresponding Java element
	 */
	abstract protected IJavaElement getCorrespondingElement(IJavaElement element);
	
	/**
	 * Sets the input of the editor's outline page.
	 * 
	 * @param page the Java outline page
	 * @param input the editor input
	 */
	abstract protected void setOutlinePageInput(JavaOutlinePage page, IEditorInput input);