Extract colors from wallpaper and dynamically update login screen overlay

ui/login/account_picker/md_screen_account_picker.js

 // Copyright 2014 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 Account picker screen implementation.
  */
 
 login.createScreen('AccountPickerScreen', 'account-picker', function() {
   /**
@@ skipping 26 matching lines @@
       'hideUserPodCustomIcon',
       'setUserPodFingerprintIcon',
       'removeUserPodFingerprintIcon',
       'setPinEnabledForUser',
       'setAuthType',
       'setTouchViewState',
       'setPublicSessionDisplayName',
       'setPublicSessionLocales',
       'setPublicSessionKeyboardLayouts',
       'setLockScreenAppsState',
+      'setOverlayColors',
     ],
 
     preferredWidth_: 0,
     preferredHeight_: 0,
 
     // Whether this screen is shown for the first time.
     firstShown_: true,
 
     // Whether this screen is currently being shown.
     showing_: false,
@@ skipping 18 matching lines @@
 
     /**
      * Sets preferred size for account picker screen.
      */
     setPreferredSize: function(width, height) {
       this.preferredWidth_ = width;
       this.preferredHeight_ = height;
     },
 
     /**
+     * Sets login screen overlay colors based on colors extracted from the
+     * wallpaper.
+     * @param {string} dmColor Color for the gradient mask.
+     * @param {string} scrollColor Color for the small pods container.
+     * @param {string} backgroundColor Color for the whole background.
+     */
+    setOverlayColors: function(dmColor, scrollColor, backgroundColor) {

[jdufault, 2017/06/12 21:37:29]

expand dm acronym 

[Wenzhao (Colin) Zang, 2017/06/12 23:40:35]

I changed it to maskColor which may make more sense for the user pod row.

+      $('pod-row').setOverlayColors(dmColor, scrollColor, backgroundColor);
+    },
+
+    /**
      * When the account picker is being used to lock the screen, pressing the
      * exit accelerator key will sign out the active user as it would when
      * they are signed in.
      */
     exit: function() {
       // Check and disable the sign out button so that we can never have two
       // sign out requests generated in a row.
       if ($('pod-row').lockedPod && !$('sign-out-user-button').disabled) {
         $('sign-out-user-button').disabled = true;
         chrome.send('signOutUser');
@@ skipping 405 matching lines @@
         return;
       }
       chrome.send('setLockScreenAppsState',
                   [LOCK_SCREEN_APPS_STATE.FOREGROUND]);
 
       event.preventDefault();
       event.stopPropagation();
     },
   };
 });