Bug 163360 [Field Assist] - API - Provide ControlDecoration constructor without specifying decoration
Currently you can only create a ControlDecoration by specifying the control and the decoration in the constructor. This works nicely when the decoration is static (ie, always content assist). But there are use cases where the decoration changes depending on the state of the field, and at creation time, it's not clear which decoration will be set. Having a constructor that doesn't require a decoration would be nice.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ControlDecoration.java
* specified, the control decoration will be positioned to the left and
	 * center of the control (<code>SWT.LEFT | SWT.CENTER</code>).
	 * </p>
	 * 
	 * @param control
	 *            the control to be decorated
	 * @param decoration
	 *            the decoration specifying the image and description to be
	 *            shown adjacent to the control.
	 * @param position
	 *            bit-wise or of position constants (<code>SWT.TOP</code>,
	 *            <code>SWT.BOTTOM</code>, <code>SWT.LEFT</code>,
	 *            <code>SWT.RIGHT</code>, and <code>SWT.CENTER</code>).
	 */
	public ControlDecoration(Control control, FieldDecoration decoration,
			int position) {
		this.position = position;
		this.decoration = decoration;
		this.control = control;
		addControlListeners();
	}
	/**
	 * Get the control that is decorated by the receiver.
	 * 
	 * @return the Control decorated by the receiver.
	 */
	public Control getControl() {
		return control;
	}
	/**