Add empty list indicator for Physical Web WebUI

components/physical_web/webui/resources/physical_web.js

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * Takes the |nearbyUrlsData| input argument which holds metadata for web pages
  * broadcast by nearby devices.
  * @param {Object} nearbyUrlsData Information about web pages broadcast by
  *      nearby devices
  */
 function renderTemplate(nearbyUrlsData) {
   // This is the javascript code that processes the template:
   jstProcess(new JsEvalContext(nearbyUrlsData), $('physicalWebTemplate'));
 }
 
 function requestNearbyURLs() {
   chrome.send('requestNearbyURLs');
 }
 
 function physicalWebItemClicked(index) {
   chrome.send('physicalWebItemClicked', [index]);
 }
 
+function clearScanNotification() {

[cco3, 2017/02/23 20:07:31]

I think the language of "notification" is a bit confusing.  Maybe we could call
this a scan indicator?

[Ran, 2017/02/23 20:59:46]

Done.

+  var scanningContainer = $('scan-container');

[cco3, 2017/02/23 20:07:31]

This selector isn't going to work.   You need the #

If we are using jquery, just use hide() or css():
$('#scan-container').hide();

same below for .show()

[Ran, 2017/02/23 20:59:46]

I was referring the "body-container". If I add the # it does not work. I don't
think it uses jquery here.

+  scanningContainer.style.visibility = 'hidden';
+}
+
 function returnNearbyURLs(nearbyUrlsData) {
   var bodyContainer = $('body-container');
   renderTemplate(nearbyUrlsData);
+  bodyContainer.style.visibility = 'visible';
 
-  bodyContainer.style.visibility = 'visible';
+  clearScanNotification();

[mattreynolds, 2017/02/23 20:18:42]

How long does it normally take to receive the URLs? Will the user realistically
have a chance to read the scanning message before it's replaced with the URL
list or empty message?

[Ran, 2017/02/23 20:59:46]

It's very fast, when I am doing test, I did't see the scanning message.

[mattreynolds, 2017/02/23 22:58:19]

With the current behavior it should always be instant since we're just pulling
the current values from the PhysicalWebDataSource and don't need to wait for any
scanning or URL resolution. I'd consider it a bug if this took long enough for
the user to read the scanning message. I think we shouldn't try to show a
message in this case since it will only be frustrating to the user, if they
notice it at all.

+  if (nearbyUrlsData['metadata'].length == 0) {
+    var emptyMessage = $('empty-container');
+    emptyMessage.style.visibility = 'visible';
+  }
 }
 
 document.addEventListener('DOMContentLoaded', requestNearbyURLs);
+document.addEventListener('DOMContentLoaded', function() {
+  setTimeout(clearScanNotification, 6000);

[cco3, 2017/02/23 20:07:31]

Since we always return nearbyurls right away, this doesn't do anything yet,
right?  If not, we should remove it.

[Ran, 2017/02/23 20:59:46]

Removed.
when I test, it gives the nearbyurls right way, just not sure if it is always
the case.

+});