code: function(chart) {
  		var cache = chart.$plugins || (chart.$plugins = {});
  		if (cache.id === this._cacheId) {
  			return cache.descriptors;
  		}
  
  		var plugins = [];
  		var descriptors = [];
  		var config = (chart && chart.config) || {};
  		var options = (config.options && config.options.plugins) || {};
  
  		this._plugins.concat(config.plugins || []).forEach(function(plugin) {
  			var idx = plugins.indexOf(plugin);
  			if (idx !== -1) {
  				return;
  			}
  
  			var id = plugin.id;
  			var opts = options[id];
  			if (opts === false) {
  				return;
  			}
  
  			if (opts === true) {
  				opts = helpers.clone(defaults.global.plugins[id]);
  			}
  
  			plugins.push(plugin);
  			descriptors.push({
  				plugin: plugin,
  				options: opts || {}
  			});
  		});
  
  		cache.descriptors = descriptors;
  		cache.id = this._cacheId;
  		return descriptors;
  	}
docs: Returns descriptors of enabled plugins for the given chart.
  @returns {object[]} [{ plugin, options }]
  @private