Bug 119340 [PopupDialog] - need constant for horizontal spacing
PopupDialog provides a constant for vertical spacing used in the contents, but not for horizontal spacing.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/PopupDialog.java
/**
	 * The dialog settings key name for stored dialog x location.
	 */
	private static final String DIALOG_ORIGIN_X = "DIALOG_X_ORIGIN"; 
	/**
	 * The dialog settings key name for stored dialog y location.
	 */
	private static final String DIALOG_ORIGIN_Y = "DIALOG_Y_ORIGIN"; 
	/**
	 * The dialog settings key name for stored dialog width.
	 */
	private static final String DIALOG_WIDTH = "DIALOG_WIDTH"; 
	/**
	 * The dialog settings key name for stored dialog height.
	 */
	private static final String DIALOG_HEIGHT = "DIALOG_HEIGHT"; 
	/**
	 * The dialog settings key name for remembering if the persisted bounds
	 * should be accessed.
	 */
	private static final String DIALOG_USE_PERSISTED_BOUNDS = "DIALOG_USE_PERSISTED_BOUNDS"; 
	/**
	 * Move action for the dialog.
	 */
	private class MoveAction extends Action {