Revert 230138 "Delay wallpaper load by 2 * average wallpaper loa..."

trunk/src/chrome/browser/resources/chromeos/login/wallpaper_loader.js

-// Copyright 2013 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.
-
-cr.define('login', function() {
-
-  /**
-   * Minimum wallpaper load delay in milliseconds.
-   * @type {number}
-   * @const
-   */
-  var WALLPAPER_LOAD_MIN_DELAY_MS = 100;
-
-  /**
-   * If last walpaper load time cannot be calculated, assume this value.
-   * @type {number}
-   * @const
-   */
-  var WALLPAPER_DEFAULT_LOAD_TIME_MS = 200;
-
-  /**
-   * Min and Max average wallpaper load time.
-   * Delay to next wallpaper load is 2 * <average load time>.
-   * @type {number}
-   * @const
-   */
-  var WALLPAPER_MIN_LOAD_TIME_MS = 50;
-  var WALLPAPER_MAX_LOAD_TIME_MS = 2000;
-
-  /**
-   * Number last wallpaper load times to remember.
-   * @type {number}
-   * @const
-   */
-  var WALLPAPER_LOAD_STATS_MAX_LENGTH = 4;
-
-
-  /**
-   * Creates a new pod row element.
-   * @constructor
-   * @extends {HTMLDivElement}
-   */
-  var WallpaperLoader = function() {
-    this.wallpaperLoadInProgress_ = {
-        name: '',
-        date: undefined
-    };
-    this.loadStats_ = [];
-  };
-
-  WallpaperLoader.prototype = {
-    // When moving through users quickly at login screen, set a timeout to
-    // prevent loading intermediate wallpapers.
-    loadWallpaperTimeout_: null,
-
-    // When waiting for wallpaper load, remember load start time.
-    // wallpaperLoadInProgress_: { name: '', date: undefined }
-    wallpaperLoadInProgress_: undefined,
-
-    // Wait a delay and then load this wallpaper. Value = username.
-    wallpaperLoadPending_: undefined,
-
-    // Wait untill this Date before loading next wallpaper.
-    wallpaperLoadTryNextAfter_: undefined,
-
-    // Username, owner of current wallpaper.
-    currentWallpaper_: '',
-
-    // Array of times (in milliseconds) of last wallpaper load attempts.
-    // Length is limited by WALLPAPER_LOAD_STATS_MAX_LENGTH.
-    loadStats_: undefined,
-
-    /**
-     * Stop load timer. Clear pending record.
-     */
-    reset: function() {
-      delete this.wallpaperLoadPending_;
-      if (this.loadWallpaperTimeout_ != null)
-        window.clearTimeout(this.loadWallpaperTimeout_);
-      this.loadWallpaperTimeout_ = null;
-    },
-
-    /**
-     * Schedules wallpaper load.
-     */
-    scheduleLoad: function(email) {
-      if (this.wallpaperLoadPending_ && this.wallpaperLoadPending_ == email)
-        return;
-      this.reset();
-      if (this.wallpaperLoadInProgress_.name == email)
-        return;
-      if ((this.wallpaperLoadInProgress_.name == '') &&
-          (this.currentWallpaper_ == email))
-        return;
-
-      this.wallpaperLoadPending_ = email;
-      var now = new Date();
-      var timeout = WALLPAPER_LOAD_MIN_DELAY_MS;
-      if (this.wallpaperLoadTryNextAfter_)
-        timeout = Math.max(timeout, this.wallpaperLoadTryNextAfter_ - now);
-
-      this.loadWallpaperTimeout_ = window.setTimeout(
-        this.loadWallpaper_.bind(this), timeout);
-     },
-
-
-    /**
-     * Loads pending wallpaper, if any.
-     * @private
-     */
-    loadWallpaper_: function() {
-      this.loadWallpaperTimeout_ = null;
-      if (!this.wallpaperLoadPending_)
-        return;
-      if (this.wallpaperLoadInProgress_.name != '')
-        return;
-      var email = this.wallpaperLoadPending_;
-      delete this.wallpaperLoadPending_;
-      if (email == this.currentWallpaper_)
-        return;
-      this.wallpaperLoadInProgress_.name = email;
-      this.wallpaperLoadInProgress_.date = new Date();
-      chrome.send('loadWallpaper', [email]);
-    },
-
-    /**
-     * Calculates average wallpaper load time.
-     */
-    calcLoadStatsAvg: function() {
-        return this.loadStats_.reduce(
-            function(previousValue, currentValue) {
-              return previousValue + currentValue;
-            }) / this.loadStats_.length;
-    },
-
-    /**
-     * Calculates average next wallpaper load delay time.
-     */
-    getWallpaperLoadTime_: function() {
-      var avg = WALLPAPER_DEFAULT_LOAD_TIME_MS;
-
-      if (this.loadStats_.length == 0)
-        return avg;
-
-      avg = this.calcLoadStatsAvg();
-      if (avg < WALLPAPER_MIN_LOAD_TIME_MS)
-        avg = WALLPAPER_MIN_LOAD_TIME_MS;
-
-      if (avg > WALLPAPER_MAX_LOAD_TIME_MS)
-        avg = WALLPAPER_MAX_LOAD_TIME_MS;
-
-      return avg;
-    },
-
-    /**
-     * Handles 'onWallpaperLoaded' event. Recalculates statistics and
-     * [re]schedules next wallpaper load.
-     */
-    onWallpaperLoaded: function(email) {
-      this.currentWallpaper_ = email;
-      if (email != this.wallpaperLoadInProgress_.name)
-          return;
-      this.wallpaperLoadInProgress_.name = '';
-      var started = this.wallpaperLoadInProgress_.date;
-      var finished = new Date();
-      var elapsed = started ? finished - started :
-          WALLPAPER_DEFAULT_LOAD_TIME_MS;
-      this.loadStats_.push(elapsed);
-      if (this.loadStats_.length > WALLPAPER_LOAD_STATS_MAX_LENGTH)
-        this.loadStats_.shift();
-
-      this.wallpaperLoadTryNextAfter_ = new Date(Date.now() + 2 *
-          this.getWallpaperLoadTime_());
-      if (this.wallpaperLoadPending_) {
-        var newWallpaperEmail = this.wallpaperLoadPending_;
-        this.reset();
-        this.scheduleLoad(newWallpaperEmail);
-      }
-    }
-  };
-
-  return {
-    WallpaperLoader: WallpaperLoader
-  };
-});