Fix scroll to added item

src/vaadin-grid-data-provider-mixin.html

@@ -201,6 +201,8 @@
       this._cache.size += delta;
       this._cache.effectiveSize += delta;
       this._effectiveSize = this._cache.effectiveSize;
+      this._increasePoolIfNeeded(0);
+      this._debounceIncreasePool && this._debounceIncreasePool.flush();
     }
 
     /**

test/physical-count.html

@@ -79,10 +79,6 @@
 
       it('increase pool size after resizing the scroller', () => {
         grid.classList.add('small');
-        // Workaround for FF58 rendering issue
-        grid.size = 0;
-        grid.size = 200;
-
         grid.style.display = 'none';
 
         expect(grid._physicalItems.length).to.eql(25);

test/scroll-to-index.html

@@ -150,6 +150,33 @@
 
       });
 
+      describe('Added item', () => {
+        let grid, scroller, data;
+
+        beforeEach(() => {
+          grid = fixture('large');
+          data = Array(...new Array(10)).map((_, i) => {
+            return {'index': i};
+          });
+
+          grid.size = 10;
+          grid.dataProvider = function(params, callback) {
+            callback(data);
+          };
+
+          flushGrid(grid);
+        });
+
+        it('should not reassign the first item on scrollToIndex', () => {
+          const newExpectedSize = grid.size + 1;
+          grid.size = newExpectedSize;
+          data.push({'index': 11});
+          grid.scrollToIndex(grid.items.length);
+
+          expect(grid.$.items.children[0]._item.index).to.equal(0);
+        });
+      });
+
     });
   </script>