Asynchronously load wallpapers when user pod is selected.

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

Index: chrome/browser/resources/chromeos/login/user_pod_row.js
diff --git a/chrome/browser/resources/chromeos/login/user_pod_row.js b/chrome/browser/resources/chromeos/login/user_pod_row.js
index 149b3175eb580fab6afd6c04f64a8ce12a7dd471..ffd42691a0d71b63e8f4c8791c131885968f68ea 100644
--- a/chrome/browser/resources/chromeos/login/user_pod_row.js
+++ b/chrome/browser/resources/chromeos/login/user_pod_row.js
@@ -7,14 +7,26 @@
  */
 
 cr.define('login', function() {
-  // Pod width. 170px Pod + 10px padding + 10px margin on both sides.
-  const POD_WIDTH = 170 + 2 * (10 + 10);
+  /**
+   * Pod width. 170px Pod + 10px padding + 10px margin on both sides.
+   * @type {number}
+   * @const
+   */
+  var POD_WIDTH = 170 + 2 * (10 + 10);
+
+  /**
+   * Wallpaper load delay in milliseconds.
+   * @type {number}
+   * @const
+   */
+  var WALLPAPER_LOAD_DELAY_MS = 800;
 
   /**
    * Oauth token status. These must match UserManager::OAuthTokenStatus.
    * @enum {number}
+   * @const
    */
-  const OAuthTokenStatus = {
+  var OAuthTokenStatus = {
     UNKNOWN: 0,
     INVALID: 1,
     VALID: 2
@@ -23,8 +35,9 @@ cr.define('login', function() {
   /**
    * Tab order for user pods.  Update these when adding new controls.
    * @enum {number}
+   * @const
    */
-  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.
@@ -457,6 +470,10 @@ cr.define('login', function() {
     // Activated pod, i.e. the pod of current login attempt.
     activatedPod_: undefined,
 
+    // When moving through users quickly at login screen, set a timeout to
+    // prevent loading intermediate wallpapers.
+    loadWallpaperTimeout_: null,
+
     // Pods whose initial images haven't been loaded yet.
     podsWithPendingImages_: [],
 
@@ -632,6 +649,7 @@ cr.define('login', function() {
       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) {
@@ -647,6 +665,9 @@ cr.define('login', function() {
         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_MS);
       }
     },