Javascript 如何在google图表中使用google.visualization.DataTable（）

我在聚合物应用程序中使用GoogleCharts的DataTable对象时遇到问题

我按如下方式加载图表元素：

<link href="/bower_components/google-apis/google-legacy-loader.html" rel="import" />
<link href="/bower_components/google-chart/google-chart.html" rel="import" />

我得到：

Uncaught TypeError: Cannot read property 'DataTable' of undefined

这里的问题是什么？

在聚合物表（或一些图表）中创建为：

<google-chart
    type="table"
    data='[["ID", "Life Expectancy", "Fertility Rate", "Region", "Population"],
           ["CAN", 80.66, 1.67, "North America", 33739900],
           ["DEU", 79.84, 1.36, "Europe",        81902307],
           ["DNK", 78.6,  1.84, "Europe",        5523095],
           ["EGY", 72.73, 2.78, "Middle East",   79716203],
           ["GBR", 80.05, 2,    "Europe",        61801570],
           ["IRN", 72.49, 1.7,  "Middle East",   73137148],
           ["IRQ", 68.09, 4.77, "Middle East",   31090763],
           ["ISR", 81.55, 2.96, "Middle East",   7485600],
           ["RUS", 68.6,  1.54, "Europe",        141850000],
           ["USA", 78.09, 2.05, "North America", 307007000]]'>
  </google-chart>

更多示例和文档链接如下：

<google-chart
    type="table"
    data='[["ID", "Life Expectancy", "Fertility Rate", "Region", "Population"],
           ["CAN", 80.66, 1.67, "North America", 33739900],
           ["DEU", 79.84, 1.36, "Europe",        81902307],
           ["DNK", 78.6,  1.84, "Europe",        5523095],
           ["EGY", 72.73, 2.78, "Middle East",   79716203],
           ["GBR", 80.05, 2,    "Europe",        61801570],
           ["IRN", 72.49, 1.7,  "Middle East",   73137148],
           ["IRQ", 68.09, 4.77, "Middle East",   31090763],
           ["ISR", 81.55, 2.96, "Middle East",   7485600],
           ["RUS", 68.6,  1.54, "Europe",        141850000],
           ["USA", 78.09, 2.05, "North America", 307007000]]'>
  </google-chart>