MD Settings: Fix iron-list losing focus when items change.

third_party/polymer/v1_0/components-chromium/iron-list/iron-list-extracted.js

 (function() {
 
   var IOS = navigator.userAgent.match(/iP(?:hone|ad;(?: U;)? CPU) OS (\d+)/);
   var IOS_TOUCH_SCROLLING = IOS && IOS[1] >= 8;
   var DEFAULT_PHYSICAL_COUNT = 3;
   var HIDDEN_Y = '-10000px';
   var ITEM_WIDTH = 0;
   var ITEM_HEIGHT = 1;
   var SECRET_TABINDEX = -100;
 
@@ skipping 108 matching lines @@
        * This value can be computed using the position returned by `getBoundingClientRect()`
        * although it's preferred to use a constant value when possible.
        *
        * This property is useful when an external scrolling element is used and there's
        * some offset between the scrolling element and the list.
        * For example: a header is placed above the list.
        */
       scrollOffset: {
         type: Number,
         value: 0
+      },
+
+      /**
+       * If set to true, focus on an element will be preserved after rerender.
+       */
+      preserveFocus: {
+        type: Boolean,
+        value: false
       }
     },
 
     observers: [
       '_itemsChanged(items.*)',
       '_selectionEnabledChanged(selectionEnabled)',
       '_multiSelectionChanged(multiSelection)',
       '_setOverflow(scrollTarget, scrollOffset)'
     ],
 
@@ skipping 749 matching lines @@
         }
         el._templateInstance[this.as] = value;
       }
     },
 
     /**
      * Called when the items have changed. That is, ressignments
      * to `items`, splices or updates to a single item.
      */
     _itemsChanged: function(change) {
+      var rendering = /^items(\.splices){0,1}$/.test(change.path);
+      var lastFocusedIndex, focusedElement;
+      if (rendering && this.preserveFocus) {
+        lastFocusedIndex = this._focusedIndex;
+        focusedElement = this.querySelector('* /deep/ *:focus');
+      }
+
+      var preservingFocus = rendering && this.preserveFocus && focusedElement;
+
       if (change.path === 'items') {
         this._virtualStart = 0;
         this._physicalTop = 0;
         this._virtualCount = this.items ? this.items.length : 0;
         this._collection = this.items ? Polymer.Collection.get(this.items) : null;
         this._physicalIndexForKey = {};
         this._firstVisibleIndexVal = null;
         this._lastVisibleIndexVal = null;
         this._physicalCount = this._physicalCount || 0;
         this._physicalItems = this._physicalItems || [];
         this._physicalSizes = this._physicalSizes || [];
         this._physicalStart = 0;
-        if (this._scrollTop > this._scrollOffset) {
+        if (this._scrollTop > this._scrollOffset && !preservingFocus) {
           this._resetScrollPosition(0);
         }
         this._removeFocusedItem();
         this._debounceTemplate(this._render);
-
       } else if (change.path === 'items.splices') {
         this._adjustVirtualIndex(change.value.indexSplices);
         this._virtualCount = this.items ? this.items.length : 0;
 
         this._debounceTemplate(this._render);
       } else {
         this._forwardItemPath(change.path.split('.').slice(1).join('.'), change.value);
       }
+
+      // If the list was in focus when updated, preserve the focus on item.
+      if (preservingFocus) {
+        Polymer.dom.flush();
+        focusedElement.blur(); // paper- elements breaks when focused twice.
+        this._focusPhysicalItem(
+            Math.min(this.items.length - 1, lastFocusedIndex));
+        if (!this._isIndexVisible(this._focusedIndex)) {
+          this.scrollToIndex(this._focusedIndex);
+        }
+      }
     },
 
     /**
      * @param {!Array<!PolymerSplice>} splices
      */
     _adjustVirtualIndex: function(splices) {
       splices.forEach(function(splice) {
         // deselect removed items
         splice.removed.forEach(this._removeItem, this);
         // We only need to care about changes happening above the current position
@@ skipping 671 matching lines @@
       this._focusPhysicalItem(this._focusedIndex + 1);
     },
 
     _didEnter: function(e) {
       this._focusPhysicalItem(this._focusedIndex);
       this._selectionHandler(e.detail.keyboardEvent);
     }
   });
 
 })();