Asynchronously load wallpapers when user pod is selected.

chrome/browser/resources/chromeos/login/user_pod_row.js

 // Copyright (c) 2012 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.
 
 /**
  * @fileoverview User pod row implementation.
  */
 
 cr.define('login', function() {
   // Pod width. 170px Pod + 10px padding + 10px margin on both sides.
-  const POD_WIDTH = 170 + 2 * (10 + 10);
+  var POD_WIDTH = 170 + 2 * (10 + 10);
+
+  // Wallpaper load delay in milliseconds.
+  var WALLPAPER_LOAD_DELAY = 800;

[Nikita (slow), 2012/04/26 17:22:03]

nit: WALLPAPER_LOAD_DELAY_MS

 
   /**
    * Oauth token status. These must match UserManager::OAuthTokenStatus.
    * @enum {number}
    */
-  const OAuthTokenStatus = {
+  var OAuthTokenStatus = {
     UNKNOWN: 0,
     INVALID: 1,
     VALID: 2
   };
 
   /**
    * Tab order for user pods.  Update these when adding new controls.
    * @enum {number}
    */
-  const UserPodTabOrder = {
+  var UserPodTabOrder = {
     POD_INPUT: 1,    // Password input fields (and whole pods themselves).
     HEADER_BAR: 2,   // Buttons on the header bar (Shutdown, Add User).
     REMOVE_USER: 3   // Remove ('X') buttons.
   };
 
   // Focus and tab order are organized as follows:
   //
   // (1) all user pods have tab index 1 so they are traversed first;
   // (2) when a user pod is activated, its tab index is set to -1 and its
   //     main input field gets focus and tab index 1;
@@ skipping 412 matching lines @@
 
   PodRow.prototype = {
     __proto__: HTMLDivElement.prototype,
 
     // Focused pod.
     focusedPod_ : undefined,
 
     // Activated pod, i.e. the pod of current login attempt.
     activatedPod_: undefined,
 
+    // When quickly move through users at login screen, we need to set a
+    // timeout to prevent loading intermediate wallpapers.
+    loadWallpaperTimeout_: null,
+
     // Pods whose initial images haven't been loaded yet.
     podsWithPendingImages_: [],
 
     /** @inheritDoc */
     decorate: function() {
       this.style.left = 0;
 
       // Event listeners that are installed for the time period during which
       // the element is visible.
       this.listeners_ = {
@@ skipping 155 matching lines @@
     /**
      * Focuses a given user pod or clear focus when given null.
      * @param {UserPod=} podToFocus User pod to focus (undefined clears focus).
      * @param {boolean=} opt_force If true, forces focus update even when
      *     podToFocus is already focused.
      */
     focusPod: function(podToFocus, opt_force) {
       if (this.focusedPod_ == podToFocus && !opt_force)
         return;
 
+      clearTimeout(this.loadWallpaperTimeout_);
       for (var i = 0, pod; pod = this.pods[i]; ++i) {
         pod.activeRemoveButton = false;
         if (pod != podToFocus) {
           pod.classList.remove('focused');
           pod.classList.remove('faded');
           pod.reset(false);
         }
       }
 
       this.focusedPod_ = podToFocus;
       if (podToFocus) {
         podToFocus.classList.remove('faded');
         podToFocus.classList.add('focused');
         podToFocus.reset(true);  // Reset and give focus.
         this.scrollPodIntoView(podToFocus);
+        this.loadWallpaperTimeout_ = window.setTimeout(function() {
+              chrome.send('userSelectedDelayed', [podToFocus.user.username]);
+            }, WALLPAPER_LOAD_DELAY);
       }
     },
 
     /**
      * Returns the currently activated pod.
      * @type {UserPod}
      */
     get activatedPod() {
       return this.activatedPod_;
     },
@@ skipping 187 matching lines @@
       if (this.podsWithPendingImages_.length == 0) {
         chrome.send('userImagesLoaded');
       }
     }
   };
 
   return {
     PodRow: PodRow
   };
 });