Bug 163461 [Field Assist] - API - ControlDecoration should work with image+text, not FieldDecoration
DecoratedField supported multiple decoration locations, so it was useful to expose a data structure that referred to a particular decoration. Hence FieldDecoration was defined. It is just an image+text data structure, but was useful for asking DecoratedField to "do things" to a particular decoration, such as hiding it, showing it, updating it, etc. The initial API for ControlDecoration also supported FieldDecoration, in an attempt to "explain itself" as being similar to DecoratedField. However, since a ControlDecoration only shows one decoration, there's not really a need for the image+text to have any kind of identity. It would be better if the ControlDecoration API worked in terms of having an image and a description text. Clients could still use FieldDecorations and the registry if desired, but the API shouldn't require it, since it's trivial to pull the image and text out of a decoration and feed it to ControlDecoration.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ControlDecoration.java
private int haw = 8;
		/**
		 * Height of info hover arrow.
		 */
		private int hah = 10;
		/**
		 * Margin around info hover text.
		 */
		private int hm = 2;
		/**
		 * This info hover's shell.
		 */
		Shell hoverShell;
		/**
		 * The info hover text.
		 */
		String text = EMPTY;
		/**
		 * The region used to manage the shell shape
		 */
		Region region;
		/**
		 * Boolean indicating whether the last computed polygon location had an
		 * arrow on left. (true if left, false if right).
		 */
		boolean arrowOnLeft = true;
		/*
		 * Create a hover parented by the specified shell.
		 */
		Hover(Shell parent) {