Bug 33550 [Dialogs] Dialog should support remembering size and position
There are several dialogs that remember its size and position. Since restore the size and considering screen size and font changes isn't trivial JFace's Dialog class should support remembering and restoring size and position. These would realy ease the task for subclasses. May be you can steel the code from OpenTypeSelectionDialog.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/Dialog.java
* The returned control's layout data must be an instance of
     * <code>GridData</code>.
     * </p>
     * 
     * @param parent
     *            the parent composite to contain the button bar
     * @return the button bar control
     */
    protected Control createButtonBar(Composite parent) {
        Composite composite = new Composite(parent, SWT.NONE);
        
        
        GridLayout layout = new GridLayout();
        layout.numColumns = 0; 
        layout.makeColumnsEqualWidth = true;
        layout.marginWidth = convertHorizontalDLUsToPixels(IDialogConstants.HORIZONTAL_MARGIN);
        layout.marginHeight = convertVerticalDLUsToPixels(IDialogConstants.VERTICAL_MARGIN);
        layout.horizontalSpacing = convertHorizontalDLUsToPixels(IDialogConstants.HORIZONTAL_SPACING);
        layout.verticalSpacing = convertVerticalDLUsToPixels(IDialogConstants.VERTICAL_SPACING);
        composite.setLayout(layout);
        GridData data = new GridData(GridData.HORIZONTAL_ALIGN_END
                | GridData.VERTICAL_ALIGN_CENTER);
        composite.setLayoutData(data);
        composite.setFont(parent.getFont());
        
        createButtonsForButtonBar(composite);
        return composite;
    }
    /**
     * Adds buttons to this dialog's button bar.