Bug 118163 [Dialogs] - PopupDialog should define constants for zero margins
PopupDialogs traditionally use a 0 margin width and height for the grid layouts used. This should be made an API constant rather than subclasses just knowing.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/PopupDialog.java
* The dialog's toolbar for the move and resize capabilities.
	 */
	private ToolBar toolBar = null;
	/**
	 * The dialog's menu manager.
	 */
	private MenuManager menuManager = null;
	/**
	 * The control representing the main dialog area.
	 */
	private Control dialogArea;
	/**
	 * Labels that contain title and info text. Cached so they can be updated
	 * dynamically if possible.
	 */
	private Label titleLabel, infoLabel;
	/**
	 * Separator controls. Cached so they can be excluded from color changes.
	 */
	private Control titleSeparator, infoSeparator;
	/**
	 * The images for the dialog menu.
	 */
	private Image menuImage, disabledMenuImage = null;
	/**
	 * Font to be used for the info area text. Computed based on the dialog's
	 * font.
	 */
	private Font infoFont;
	/**