MD User Manager: Display error message when all profiles are locked.

chrome/browser/resources/md_user_manager/user_manager.js

Index: chrome/browser/resources/md_user_manager/user_manager.js
diff --git a/chrome/browser/resources/md_user_manager/user_manager.js b/chrome/browser/resources/md_user_manager/user_manager.js
index 6864f2c15aee827e7fb3d549e0cf1d4bd0b9f64e..24e329aedb5316dda10467e342773947191324b1 100644
--- a/chrome/browser/resources/md_user_manager/user_manager.js
+++ b/chrome/browser/resources/md_user_manager/user_manager.js
@@ -66,6 +66,7 @@ cr.define('cr.ui', function() {
 
     signin.ProfileBrowserProxyImpl.getInstance().initializeUserManager(
         window.location.hash);
+    cr.addWebUIListener('show-error-dialog', cr.ui.UserManager.showErrorDialog);

[dpapad, 2016/05/31 19:11:59]

Should this listener be removed at some point? Is there any way the 'initialize'
method is executed twice and we end up with two or more listeners?

Polymer code solves this issue by using WebUIListenerBehavior which
automatically removes listeners within the "detached" lifecyle method. See
example at
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/res....

[Moe, 2016/05/31 20:53:05]

user_manager.js is executed in the top level html and initialize() is called on
DOMContentLoaded which is expected to be called only once during the lifetime of
chrome://md-user-manager/. Since we expect the listener to be around as long as
the page lives can we not bother with detaching it at all?

similarly, if the component, once attached, is meant to stick around during the
lifetime of the page do we have to use WebUIListenerBehavior to detach the
listeners?

[dpapad, 2016/05/31 21:05:51]

If it is guaranteed that initialized() is called only once, then it is fine to
never remove the listener. Perhaps adding a very short comment can save future
readers some time.
// Listener is purposefully active for the lifetime of this page.


Regarding Polymer components, it is OK to never remove it if the component is
never detached, but it also does not hurt to always use the
WebUIListenerBehavior. It makes it more robust to future optimizations where a
component is removed from the DOM when not visible. For example in md_settings,
which is a fairly large page, several things are removed from the DOM when not
needed. This is especially true for listeners registered by dialogs.

   };
 
   /**
@@ -132,6 +133,14 @@ cr.define('cr.ui', function() {
     DisplayManager.clearErrors();
   };
 
+  /**
+   * Shows the error dialog populated with the given message.
+   * @param {string} message Error message to show.
+   */
+  UserManager.showErrorDialog = function(message) {
+    document.querySelector('error-dialog').show(message);
+  };
+
   // Export
   return {
     UserManager: UserManager