Bug 295386 [FieldAssist] ControlDecoration#showHoverText doesn't check if the widget is visible
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ControlDecoration.java
private static final String EMPTY = ""; 
		/**
		 * Offset of info hover arrow from the left or right side.
		 */
		private int hao = 10;