fix(virtual-repeat): Prevent nested calls to virtualRepeatUpdate_

Due to some browser issues, the $watchCollection callback that calls
virtualRepeatUpdate_ sometimes fires in the middle of a
virtualRepeatUpdate_ call. This can result in duplicate items showing up
in the virtual repeat list.

Fixes #4950. Closes #5009.

Author: Michael Chen

src/components/virtualRepeat/virtual-repeater.js

@@ -422,6 +422,12 @@ function VirtualRepeatController($scope, $element, $attrs, $browser, $document,
   /** @type {boolean} Whether this is the first time that items are rendered. */
   this.isFirstRender = true;
 
+  /**
+   * @private {boolean} Whether the items in the list are already being updated. Used to prevent
+   *     nested calls to virtualRepeatUpdate_.
+   */
+  this.isVirtualRepeatUpdating_ = false;
+
   /** @type {number} Most recently seen length of items. */
   this.itemsLength = 0;
 
@@ -543,7 +549,11 @@ VirtualRepeatController.prototype.containerUpdated = function() {
     this.unwatchItemSize_();
     this.sized = true;
     this.$scope.$watchCollection(this.repeatListExpression,
-        angular.bind(this, this.virtualRepeatUpdate_));
+        angular.bind(this, function(items, oldItems) {
+          if (!this.isVirtualRepeatUpdating_) {
+            this.virtualRepeatUpdate_(items, oldItems);
+          }
+        }));
   }
 
   this.updateIndexes_();
@@ -574,6 +584,8 @@ VirtualRepeatController.prototype.getItemSize = function() {
  * @private
  */
 VirtualRepeatController.prototype.virtualRepeatUpdate_ = function(items, oldItems) {
+  this.isVirtualRepeatUpdating_ = true;
+
   var itemsLength = items && items.length || 0;
   var lengthChanged = false;
 
@@ -664,6 +676,8 @@ VirtualRepeatController.prototype.virtualRepeatUpdate_ = function(items, oldItem
 
   this.startIndex = this.newStartIndex;
   this.endIndex = this.newEndIndex;
+
+  this.isVirtualRepeatUpdating_ = false;
 };