Add top level app element

appengine/swarming/elements/res/imp/stats/partial-line-chart.html

 <!--
 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed by the Apache v2.0 license that can be
 # found in the LICENSE file.
 -->
 <!--
   This in an HTML Import-able file that contains the definition
   of the following elements:
 
     <partial-line-chart>
@@ skipping 11 matching lines @@
     names: Array<String>, the names of the data columns to show.  If blank,
         all will be shown.
     title: String, the title of the line graph.
 
   Methods:
     None.
 
   Events:
     None.
 -->
-<link rel="import" href="../bower_components/google-chart/google-chart.html">
+<link rel="import" href="/imp/bower_components/google-chart/google-chart.html">
 
 <dom-module id="partial-line-chart">
   <style>
     google-chart {
       width: 100%;
       height: 250px;
     }
   </style>
   <template>
 
@@ skipping 59 matching lines @@
           }
         }
 
         view.setColumns(colsToShow);
         return JSON.parse(view.toDataTable().toJSON());
       },
     });
   })();
   </script>
 </dom-module>