public void selectAll() {
        int length = getText().length();
        if (length > 0) {
            setSelectionRange(0, length);
        }
    }
Selects all of the text in the box.
<p>
This will only work when the widget is attached to the document and not
hidden.
stroom-core-client-widget/src/main/java/com/google/gwt/user/client/ui/ValueBoxBase.java