An array of objects can be assigned to the items property.
The items property can be modified using Polymer's array mutation methods.
Setting height-by-rows will make <vaadin-grid> grow
and shrink in height depending on the number of rows.
A function can be assigned to the dataProvider property to provide
data from a remote source.
Note: the total number of items must be set to the grid. The example
below sets the total number of items using the size property.
Alternatively, the total size can be provided in the second argument of the
data provider callback, see tree demo example.