Bug 129214 [Field Assist] - Decorated Field attachments not centering images horizontally
DecoratedField is supposed to center decorations horizontally on each side. The current attachments are not doing so. Also consider whether grid would have been a better choice for internal implementation.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/DecoratedField.java
e.y - b, 0, e.y - b, 0, 0 };
			return new int[] { 0, 0, e.x - b, 0, e.x - b, e.y - b,
					e.x - hao - b, e.y - b, e.x - hao - haw / 2, e.y + hah - b,
					e.x - hao - haw, e.y - b, 0, e.y - b, 0, 0 };
		}
		/*
		 * Dispose the hover, it is no longer needed. Dispose any resources
		 * allocated by the hover.
		 */
		void dispose() {
			if (!hoverShell.isDisposed())
				hoverShell.dispose();
			if (region != null) {
				region.dispose();
			}
		}
		/*
		 * Set the visibility of the hover.
		 */
		void setVisible(boolean visible) {
			if (visible) {
				if (!hoverShell.isVisible())
					hoverShell.setVisible(true);
			} else {
				if (hoverShell.isVisible())
					hoverShell.setVisible(false);
			}
		}
		/*
		 * Set the text of the hover to the specified text. Recompute the size