Bug 12329 [Cell Editors] Request:ComboBoxCellEditor READ_ONLY style
Although CCombo accepts SWT.READ_ONLY style, there is no way to specify style when it is used in ComboBoxCellEditor. How about adding createControl(Composite parent, int style) method to ComboBoxCellEditor class?
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/DialogCellEditor.java
* The cell editor value is <code>null</code> initially, and has no 
 * validator.
 *
 * @param parent the parent control
 */
protected DialogCellEditor(Composite parent) {
	super(parent);
}
/**
 * Creates the button for this cell editor under the given parent control.
 * <p>
 * The default implementation of this framework method creates the button 
 * display on the right hand side of the dialog cell editor. Subclasses
 * may extend or reimplement.
 * </p>
 *
 * @param parent the parent control
 * @return the new button control
 */
protected Button createButton(Composite parent) {
	Button result = new Button(parent, SWT.DOWN);
	result.setText("..."); 
	return result;
}
/**
 * Creates the controls used to show the value of this cell editor.
 * <p>
 * The default implementation of this framework method creates
 * a label widget, using the same font and background color as the parent control.
 * </p>