Constructs a WidgetPluginManager object.
\Traversable $namespaces: An object that implements \Traversable which contains the root paths keyed by the corresponding namespace to look for plugin implementations,
public function __construct(\Traversable $namespaces) {
$this->discovery = new AnnotatedClassDiscovery('field/widget', $namespaces);
$this->discovery = new ProcessDecorator($this->discovery, array(
$this,
'processDefinition',
));
$this->discovery = new AlterDecorator($this->discovery, 'field_widget_info');
$this->discovery = new CacheDecorator($this->discovery, 'field_widget_types', 'field');
$this->factory = new WidgetFactory($this->discovery);
}