Make the buttons on task-page work

appengine/swarming/elements/res/js/common.js

 // 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.swarming = this.swarming || function() {
 
   var swarming = {};
 
   // naturalCompare tries to use natural sorting (e.g. sort ints by value).
   swarming.naturalCompare = function(a, b) {
@@ skipping 35 matching lines @@
       var c = comp(a, b);
       if (c === 0) {
         return a.__sortIdx - b.__sortIdx;
       }
       return c;
     });
   }
 
   // postWithToast makes a post request and updates the error-toast
   // element with the response, regardless of failure.  See error-toast.html
-  // for more information.
-  swarming.postWithToast = function(url, msg, auth_headers) {
+  // for more information. The body param should be an object or undefined.
+  swarming.postWithToast = function(url, msg, auth_headers, body) {
     // Keep toast displayed until we hear back from the request.
     sk.errorMessage(msg, 0);
 
-    sk.request("POST", url, undefined, auth_headers).then(function(response) {
+    auth_headers["content-type"] = "application/json; charset=UTF-8";
+    if (body) {
+      body = JSON.stringify(body);
+    }
+
+    return sk.request("POST", url, body, auth_headers).then(function(response) {
       sk.errorMessage("Request sent.  Response: "+response, 3000);
+      return response;
     }).catch(function(reason) {
       console.log("Request failed", reason);
       sk.errorMessage("Request failed.  Reason: "+reason, 5000);
+      return Promise.reject(reason);
     });
   }
 
   return swarming;
 }();