* Constructs a new instance of this class given its parent, a style value describing its behavior and appearance, and default text
*
* The style value is either one of the style constants defined in class SWT which is applicable to instances of this class, or must be built by bitwise OR'ing together (that is, using the int "|" operator) two or more of those SWT style constants. The class description lists the style constants that are applicable to the class. Style bits are also inherited from superclasses.
*
* The default text is displayed when no options are selected.
*
* @param parent a composite control which will be the parent of the new instance (cannot be null)
* @param style the style of control to construct
* @param trigger the Control listening for a mousedown to show the combo
* @throws IllegalArgumentException if the parent is null
* @throws IllegalArgumentException if the defaultText is null
* @throws SWTException if not called from the thread that created the parent