Add filter to task-list

appengine/swarming/elements/res/imp/common/common-behavior.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.
 
   It contains the definition of the following Behaviors:
 
     SwarmingBehaviors.CommonBehavior
 
   To use it, include
       behaviors: [SwarmingBehaviors.CommonBehavior]
   in the creation of any Polymer element.
 
-  SwarmingBehaviors.CommonBehavior contains shared functions to ease
-  templating, such as _or() and _not().
+  SwarmingBehaviors.CommonBehavior contains shared methods to ease
+  templating, such as _or() and _not() as well as general utility methods
+  such as _getJsonAsync.
  -->
 
 <script>
   window.SwarmingBehaviors = window.SwarmingBehaviors || {};
   (function(){
     // This behavior wraps up all the shared swarming functionality.
     SwarmingBehaviors.CommonBehavior = {
 
+      // _getJsonAsync makes an XHR to a url, parses the response as JSON
+      // and sticks the resulting object into the property with the name given
+      // by "bindTo". If busy is defined, the property with that name will be
+      // set to true while the request is in flight and false afterwards.
+      // request headers (e.g. authentication) and query params will be used if
+      // provided. Query params is an object like {String:Array<String>}. On
+      // error, bindTo will be set to false.  It is not set to undefined
+      // because computed values in Polymer don't fire if a property is
+      // undefined. Clients should check that bindTo is not falsey.
+       _getJsonAsync: function(bindTo, url, busy, headers, params) {
+        if (!bindTo || !url) {
+          console.log("Need at least a polymer element to bind to and a url");
+          return;
+        }
+        if (busy) {
+          this.set(busy, true);
+        }
+        url = url + "?" + sk.query.fromParamSet(params);
+        sk.request("GET", url, "", headers).then(JSON.parse).then(function(json){
+          this.set(bindTo, json);
+          if (busy) {
+            this.set(busy, false);
+          }
+        }.bind(this)).catch(function(reason){
+          console.log("Reason for failure of request to " + url, reason);
+          this.set(bindTo, false);
+          if (busy) {
+            this.set(busy, false);
+          }
+        }.bind(this));
+      },
+
       _not: function(a) {
         return !a;
       },
 
       _or: function() {
         var result = false;
         // can't use .foreach, as arguments isn't really an Array.
         for (var i = 0; i < arguments.length; i++) {
           result = result || arguments[i];
         }
         return result;
       },
     };
   })();
 </script>