Roll Polymer to 1.3.1

third_party/polymer/v1_0/components-chromium/iron-selector/iron-multi-selectable-extracted.js

 /** @polymerBehavior Polymer.IronMultiSelectableBehavior */
   Polymer.IronMultiSelectableBehaviorImpl = {
     properties: {
 
       /**
        * If true, multiple selections are allowed.
        */
       multi: {
         type: Boolean,
         value: false,
@@ skipping 14 matching lines @@
        */
       selectedItems: {
         type: Array,
         readOnly: true,
         notify: true
       },
 
     },
 
     observers: [
-      '_updateSelected(attrForSelected, selectedValues)'
+      '_updateSelected(selectedValues)'
     ],
 
     /**
      * Selects the given value. If the `multi` property is true, then the selected state of the
      * `value` will be toggled; otherwise the `value` will be selected.
      *
      * @method select
      * @param {string|number} value the value to select.
      */
     select: function(value) {
@@ skipping 10 matching lines @@
 
     multiChanged: function(multi) {
       this._selection.multi = multi;
     },
 
     get _shouldUpdateSelection() {
       return this.selected != null ||
         (this.selectedValues != null && this.selectedValues.length);
     },
 
+    _updateAttrForSelected: function() {
+      if (!this.multi) {
+        Polymer.IronSelectableBehavior._updateAttrForSelected.apply(this);
+      } else if (this._shouldUpdateSelection) {
+        this.selectedValues = this.selectedItems.map(function(selectedItem) {
+          return this._indexToValue(this.indexOf(selectedItem));        
+        }, this).filter(function(unfilteredValue) {
+          return unfilteredValue != null;
+        }, this);
+      }
+    },
+
     _updateSelected: function() {
       if (this.multi) {
         this._selectMulti(this.selectedValues);
       } else {
         this._selectSelected(this.selected);
       }
     },
 
     _selectMulti: function(values) {
-      this._selection.clear();
       if (values) {
-        for (var i = 0; i < values.length; i++) {
-          this._selection.setItemSelected(this._valueToItem(values[i]), true);
+        var selectedItems = this._valuesToItems(values);
+        // clear all but the current selected items
+        this._selection.clear(selectedItems);
+        // select only those not selected yet
+        for (var i = 0; i < selectedItems.length; i++) {
+          this._selection.setItemSelected(selectedItems[i], true);
         }
+      } else {
+        this._selection.clear();
       }
     },
 
     _selectionChange: function() {
       var s = this._selection.get();
       if (this.multi) {
         this._setSelectedItems(s);
       } else {
         this._setSelectedItems([s]);
         this._setSelectedItem(s);
       }
     },
 
     _toggleSelected: function(value) {
       var i = this.selectedValues.indexOf(value);
       var unselected = i < 0;
       if (unselected) {
         this.push('selectedValues',value);
       } else {
         this.splice('selectedValues',i,1);
       }
       this._selection.setItemSelected(this._valueToItem(value), unselected);
+    },
+
+    _valuesToItems: function(values) {
+      return (values == null) ? null : values.map(function(value) {
+        return this._valueToItem(value);
+      }, this);
     }
   };
 
   /** @polymerBehavior */
   Polymer.IronMultiSelectableBehavior = [
     Polymer.IronSelectableBehavior,
     Polymer.IronMultiSelectableBehaviorImpl
   ];