Bug 80429 [Preferences] [Dialogs] FieldEditors should relax requirements to support DialogPages
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/FieldEditor.java
*/
    protected abstract void adjustForNumColumns(int numColumns);
    /**
     * Applies a font.
     * <p>
     * The default implementation of this framework method
     * does nothing. Subclasses should override this method
     * if they want to change the font of the SWT control to
     * a value different than the standard dialog font.
     * </p>
     */
    protected void applyFont() {
    }
    /**
     * Checks if the given parent is the current parent of the
     * supplied control; throws an (unchecked) exception if they
     * are not correctly related.
     *
     * @param control the control
     * @param parent the parent control
     */
    protected void checkParent(Control control, Composite parent) {
        Assert.isTrue(control.getParent() == parent, "Different parents");
    }
    /**
     * Clears the error message from the message line.
     */
    protected void clearErrorMessage() {
        if (page != null)
            page.setErrorMessage(null);