Bug 273330 [JFace] Add API to MessageDialog to enable clients to use SWT.SHEET
A new style constant SWT.SHEET was added recently. Without adding new API in JFace, clients who are currently using the convenience methods MessageDialog.openWarning/Error/Information/Question/Confirmation would not be able to open these dialogs as sheets.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/MessageDialogWithToggle.java
* button.
     * 
     * @param prefKey
     *            The prefKey to set. If this value is <code>null</code>,
     *            then no preference will be modified.
     */
    public void setPrefKey(String prefKey) {
        this.prefKey = prefKey;
    }
    /**
     * A mutator for the preference store to be modified by the toggle button.
     * 
     * @param prefStore
     *            The prefStore to set. If this value is <code>null</code>,
     *            then no preference will be modified.
     */
    public void setPrefStore(IPreferenceStore prefStore) {
        this.prefStore = prefStore;
    }
    /**
     * A mutator for the button providing the toggle option. If the button
     * exists, then it will automatically get the text set to the current toggle
     * message, and its selection state set to the current selection state.
     * 
     * @param button
     *            The button to use; must not be <code>null</code>.
     */
    protected void setToggleButton(Button button) {
        if (button == null) {
            throw new NullPointerException(