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
/**
		 * Creates a new delete previous sub-word action.
		 */
		public DeletePreviousSubWordAction() {
			super(ST.DELETE_WORD_PREVIOUS);
		}
		/*
		 * @see org.eclipse.jdt.internal.ui.javaeditor.JavaEditor.PreviousSubWordAction#setCaretPosition(int)
		 */
		protected void setCaretPosition(int position) {
			if (!validateEditorInputState())
				return;
			
			final int length;
			final ISourceViewer viewer= getSourceViewer();
			Point selection= viewer.getSelectedRange();
			if (selection.y != 0) {
				position= selection.x;
				length= selection.y;