Roll third_party/polymer.

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 MAX_PHYSICAL_COUNT = 500;
   var HIDDEN_Y = '-10000px';
 
   Polymer({
 
@@ skipping 83 matching lines @@
       '_setOverflow(scrollTarget)'
     ],
 
     behaviors: [
       Polymer.Templatizer,
       Polymer.IronResizableBehavior,
       Polymer.IronA11yKeysBehavior,
       Polymer.IronScrollTargetBehavior
     ],
 
-    listeners: {
-      'iron-resize': '_resizeHandler'
-    },
-
     keyBindings: {
       'up': '_didMoveUp',
       'down': '_didMoveDown',
       'enter': '_didEnter'
     },
 
     /**
      * The ratio of hidden tiles that should remain in the scroll direction.
      * Recommended value ~0.5, so it will distribute tiles evely in both directions.
      */
@@ skipping 283 matching lines @@
       return this;
     },
 
     ready: function() {
       this.addEventListener('focus', this._didFocus.bind(this), true);
     },
 
     attached: function() {
       this.updateViewportBoundaries();
       this._render();
+      // `iron-resize` is fired when the list is attached if the event is added
+      // before attached causing unnecessary work.
+      this.listen(this, 'iron-resize', '_resizeHandler');
     },
 
     detached: function() {
       this._itemsRendered = false;
+      this.unlisten(this, 'iron-resize', '_resizeHandler');
     },
 
     /**
      * Set the overflow property if this element has its own scrolling region
      */
     _setOverflow: function(scrollTarget) {
       this.style.webkitOverflowScrolling = scrollTarget === this ? 'touch' : '';
       this.style.overflow = scrollTarget === this ? 'auto' : '';
     },
 
@@ skipping 100 matching lines @@
           currentRatio += tileHeight / hiddenContentSize;
 
           this._physicalTop += tileHeight;
           recycledTileSet.push(kth);
           recycledTiles++;
           kth = (kth + 1) % this._physicalCount;
         }
       }
 
       if (recycledTiles === 0) {
-        // If the list ever reach this case, the physical average is not significant enough
-        // to create all the items needed to cover the entire viewport.
-        // e.g. A few items have a height that differs from the average by serveral order of magnitude.
+        // Try to increase the pool if the list's client height isn't filled up with physical items
         if (physicalBottom < scrollBottom || this._physicalTop > scrollTop) {
-          this.async(this._increasePool.bind(this, 1));
+          this._increasePoolIfNeeded();
         }
       } else {
         this._virtualStart = this._virtualStart + recycledTiles;
         this._physicalStart = this._physicalStart + recycledTiles;
         this._update(recycledTileSet, movingUp);
       }
     },
 
     /**
      * Update the list of items, starting from the `_virtualStart` item.
@@ skipping 34 matching lines @@
         // First element child is item; Safari doesn't support children[0]
         // on a doc fragment
         physicalItems[i] = inst.root.querySelector('*');
         Polymer.dom(this).appendChild(inst.root);
       }
       return physicalItems;
     },
 
     /**
      * Increases the pool of physical items only if needed.
-     * This function will allocate additional physical items
-     * if the physical size is shorter than `_optPhysicalSize`
+     *
+     * @return {boolean} True if the pool was increased.
      */
     _increasePoolIfNeeded: function() {
-      if (this._viewportSize === 0 || this._physicalSize >= this._optPhysicalSize) {
+      // Base case 1: the list has no size.
+      if (this._viewportSize === 0) {
         return false;
       }
-      // 0 <= `currentPage` <= `_maxPages`
+      // Base case 2: If the physical size is optimal and the list's client height is full
+      // with physical items, don't increase the pool.
+      var isClientHeightFull = this._physicalBottom >= this._scrollBottom && this._physicalTop <= this._scrollPosition;
+      if (this._physicalSize >= this._optPhysicalSize && isClientHeightFull) {
+        return false;
+      }
+      // this value should range between [0 <= `currentPage` <= `_maxPages`]
       var currentPage = Math.floor(this._physicalSize / this._viewportSize);
+
       if (currentPage === 0) {
         // fill the first page
         this._debounceTemplate(this._increasePool.bind(this, Math.round(this._physicalCount * 0.5)));
-      } else if (this._lastPage !== currentPage) {
+      } else if (this._lastPage !== currentPage && isClientHeightFull) {
         // paint the page and defer the next increase
         // wait 16ms which is rough enough to get paint cycle.
         Polymer.dom.addDebouncer(this.debounce('_debounceTemplate', this._increasePool.bind(this, 1), 16));
       } else {
         // fill the rest of the pages
         this._debounceTemplate(this._increasePool.bind(this, 1));
       }
+
       this._lastPage = currentPage;
+
       return true;
     },
 
     /**
      * Increases the pool size.
      */
     _increasePool: function(missingItems) {
       var nextPhysicalCount = Math.min(
           this._physicalCount + missingItems,
           this._virtualCount - this._virtualStart,
@@ skipping 25 matching lines @@
     /**
      * Render a new list of items. This method does exactly the same as `update`,
      * but it also ensures that only one `update` cycle is created.
      */
     _render: function() {
       var requiresUpdate = this._virtualCount > 0 || this._physicalCount > 0;
 
       if (this.isAttached && !this._itemsRendered && this._isVisible && requiresUpdate) {
         this._lastPage = 0;
         this._update();
-        this._scrollHandler();
         this._itemsRendered = true;
       }
     },
 
     /**
      * Templetizes the user template.
      */
     _ensureTemplatized: function() {
       if (!this.ctor) {
         // Template instance props that should be excluded from forwarding
@@ skipping 74 matching lines @@
       var idx = this._physicalIndexForKey[key];
       var el = this._physicalItems[idx];
 
 
       if (idx === this._focusedIndex && this._offscreenFocusedItem) {
         el = this._offscreenFocusedItem;
       }
       if (!el) {
         return;
       }
-        
+
       inst = el._templateInstance;
 
       if (inst.__key__ !== key) {
         return;
       }
       if (dot >= 0) {
         path = this.as + '.' + path.substring(dot+1);
         inst.notifyPath(path, value, true);
       } else {
         inst[this.as] = value;
@@ skipping 263 matching lines @@
       while (currentVirtualItem < idx && targetOffsetTop < hiddenContentSize) {
         targetOffsetTop = targetOffsetTop + this._physicalSizes[currentTopItem];
         currentTopItem = (currentTopItem + 1) % this._physicalCount;
         currentVirtualItem++;
       }
       // update the scroller size
       this._updateScrollerSize(true);
       // update the position of the items
       this._positionItems();
       // set the new scroll position
-      this._resetScrollPosition(this._physicalTop + this._scrollerPaddingTop + targetOffsetTop + 1);
+      this._resetScrollPosition(this._physicalTop + this._scrollerPaddingTop + targetOffsetTop);
       // increase the pool of physical items if needed
       this._increasePoolIfNeeded();
       // clear cached visible index
       this._firstVisibleIndexVal = null;
       this._lastVisibleIndexVal = null;
     },
 
     /**
      * Reset the physical average and the average count.
      */
     _resetAverage: function() {
       this._physicalAverage = 0;
       this._physicalAverageCount = 0;
     },
 
     /**
      * A handler for the `iron-resize` event triggered by `IronResizableBehavior`
      * when the element is resized.
      */
     _resizeHandler: function() {
       // iOS fires the resize event when the address bar slides up
       if (IOS && Math.abs(this._viewportSize - this._scrollTargetHeight) < 100) {
         return;
       }
-      this._debounceTemplate(function() {
-        this._render();
-        if (this._itemsRendered && this._physicalItems && this._isVisible) {
-          this._resetAverage();
-          this.updateViewportBoundaries();
-          this.scrollToIndex(this.firstVisibleIndex);
-        }
-      });
+      // In Desktop Safari 9.0.3, if the scroll bars are always shown, 
+      // changing the scroll position from a resize handler would result in 
+      // the scroll position being reset. Waiting 1ms fixes the issue. 
+      Polymer.dom.addDebouncer(this.debounce('_debounceTemplate',
+        function() {
+          this._render();
+
+          if (this._itemsRendered && this._physicalItems && this._isVisible) {
+            this._resetAverage();
+            this.updateViewportBoundaries();
+            this.scrollToIndex(this.firstVisibleIndex);
+          }
+        }.bind(this), 1));
     },
 
     _getModelFromItem: function(item) {
       var key = this._collection.getKey(item);
       var pidx = this._physicalIndexForKey[key];
 
       if (pidx != null) {
         return this._physicalItems[pidx]._templateInstance;
       }
       return null;
@@ skipping 301 matching lines @@
       this._focusPhysicalItem(this._focusedIndex + 1);
     },
 
     _didEnter: function(e) {
       this._focusPhysicalItem(this._focusedIndex);
       this._selectionHandler(e.detail.keyboardEvent);
     }
   });
 
 })();