Add filter to task-list

appengine/swarming/elements/res/imp/botlist/bot-list.html

 <!--
   Copyright 2016 The LUCI Authors. All rights reserved.
   Use of this source code is governed under the Apache License, Version 2.0
   that can be found in the LICENSE file.
 
   This in an HTML Import-able file that contains the definition
   of the following elements:
 
     <bot-list>
 
@@ skipping 216 matching lines @@
       "device_type": "Device Type",
       "disk_space": "Free Space (MB)",
       "gpu": "GPU",
       "os": "OS",
       "pool": "Pool",
       "status": "Status",
       "xcode_version": "XCode Version",
     };
 
     var columnMap = {
+      android_devices: function(bot) {
+        var devs = this._attribute(bot, "android_devices", "0");
+        if (this._verbose) {
+          return devs.join(" | ") + " devices available";
+        }
+        // max() works on strings as long as they can be coerced to Number.
+        return Math.max(...devs) + " devices available";
+      },
       disk_space: function(bot) {
         var aliased = [];
         bot.disks.forEach(function(disk){
           var alias = sk.human.bytes(disk.mb, swarming.MB);
           aliased.push(swarming.alias.apply(disk.mb, disk.id + " "+ alias));
         }.bind(this));
         if (this._verbose) {
           return aliased.join(" | ");
         }
         return aliased[0];
@@ skipping 146 matching lines @@
         if (data && data.task_id) {
           return "/user/task/" + data.task_id;
         }
         return undefined;
       }
 
     });
   })();
   </script>
 </dom-module>