Fix task-page docs and clarify output returning nothing

appengine/swarming/ui/res/imp/taskpage/task-page.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:
 
     <task-page>
 
@@ skipping 481 matching lines @@
               </paper-input>
             </div>
 
             <template is="dom-if" if="[[_supportsMilo(_request,_show_raw)]]">
               <div class="milo tabbed" hidden$="[[_isSummaryLink(task_id)]]">
                 Milo results are only generated for task summaires, that is, tasks whose ids end in 0.  Tasks ending in 1 or 2 represent possible retries of tasks.  See <a href="//goo.gl/LE4rwV">the docs</a> for more.
               </div>
               <iframe id="miloFrame" class="milo tabbed" src$="[[_getDisplayServerLink(_server_details.display_server_url_template,task_id)]]"></iframe>
             </template>
             <template is="dom-if" if="[[_show_raw]]">
-              <div class="code stdout tabbed">[[_stdout]]</div>
+              <div class="code stdout tabbed">[[_rawOutput(_stdout,_result)]]</div>
             </template>
           </div>
         </div>
       </div>
     </swarming-app>
 
     <paper-dialog id="prompt" modal on-iron-overlay-closed="_promptClosed">
       <h2>Are you sure?</h2>
       <div>Are you sure you want to [[_dialog_prompt]]?</div>
       <div class="buttons">
@@ skipping 117 matching lines @@
         return packages;
       },
 
       _disambiguate: function(taskId, result) {
         if (!taskId.endsWith("0") || !result) {
           return false;
         }
         return result.try_number > 1;
       },
 
+      _empty: function(array) {
+        return !array || array.length == 0;
+      },
+
       _expires: function(request) {
         var delta = parseInt(request.expiration_secs);
         if (delta) {
           return sk.human.localeTime(new Date(request.created_ts.getTime() + delta * 1000));
         }
         // Fall back to something
         return request.expiration_secs + " seconds from created time";
       },
 
       _extraArgs: function(request) {
@@ skipping 66 matching lines @@
       _promptCancel: function() {
         this.set("_dialog_prompt", "cancel task "+this.task_id);
         this.$.prompt.open();
       },
 
       _promptRetry: function() {
         this.set("_dialog_prompt", "retry task "+this.task_id);
         this.$.prompt.open();
       },
 
+      _rawOutput: function(stdout, result) {
+        if (stdout) {
+          return stdout;
+        }
+        if (result.state === "PENDING" || result.state === "RUNNING") {
+          return "[No output yet]";
+        }
+        return "[No output received]";
+      },
+
       _refresh: function() {
         this.$.data.reload();
       },
 
       _requestUpdated: function(request) {
         if (this._noMilo(request)) {
           this.set("_show_raw", 1);
         }
       },
 
@@ skipping 35 matching lines @@
             console.log("Task could not be retried", e);
           }
         );
       },
 
       _rowspan: function(dims) {
         dims = dims || [];
         return dims.length + 1;
       },
 
-      _empty: function(array) {
-        return !array || array.length == 0;
-      },
-
       _supportsMilo: function(request, showRaw) {
         return !showRaw && request && this._tag(request, "allow_milo");
       },
 
-
-
       _toggleDetails: function() {
         this.set("_request_detail", !this._request_detail);
       },
 
       _tag: function(result, col) {
         if (!result || !result.tagMap) {
           return undefined;
         }
         return result.tagMap[col];
       },
 
       _wasPickedUp: function(result) {
         return result && result.state !== this.PENDING && result.state !== this.CANCELED && result.state != this.EXPIRED;
       },
 
       _wasNotPickedUp: function(result) {
         return result && !this._wasPickedUp(result);
       },
     });
   })();
   </script>
 </dom-module>