Extract colors from wallpaper and dynamically update login screen overlay

ui/login/account_picker/md_user_pod_row.css

 /* 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.
  *
  * This is the stylesheet used by user pods row of account picker UI.
  */
 
 podrow {
   /* Temporarily disabled because animation interferes with updating screen's
    size. */
@@ skipping 72 matching lines @@
 .user-image-container {
   align-items: center;
   display: flex;
   height: 100%;
   justify-content: center;
   width: 100%;
 }
 
 .user-image {
   border-radius: 50%;
-  box-shadow: 0 0 2px rgba(255, 255, 255, .34);
+  box-shadow: 0 0 4px rgba(255, 255, 255, .34);
   height: 100%;
   width: 100%;
 }
 
 .user-image.switch-image-animation {
   animation: switch-image 180ms;
 }
 
 .pod .user-image {
   flex: none;
@@ skipping 99 matching lines @@
 }
 
 .pod.focused.multiprofiles-policy-applied .name-container {
   display: flex;
 }
 
 .name {
   color: #FFFFFF;
   /* This should be 15.6px - the equivalent of 14px at 90% scale. */
   flex: auto;
-  font-family: "Roboto";
-  font-size: 24px;
+  font: 24px Roboto, sans-serif;
   outline: none;
   overflow: hidden;
   text-align: center;
   text-overflow: ellipsis;
   white-space: nowrap;
 }
 
 .auth-container,
 .password-entry-container,
 .reauth-hint-container {
@@ skipping 877 matching lines @@
 }
 
 .small-pod.extra-small .small-user-image-container {
   height: 60px;
   width: 60px;
 }
 
 .small-pod-name {
   color: #FFFFFF;
   flex: auto;
-  font-family: "Roboto";
-  font-size: 20px;
+  font: 20px Roboto, sans-serif;
   height: 28px;
   left: 90px;
   opacity: 1;
   outline: none;
   overflow: hidden;
   padding: 23px 0;
   position: absolute;
   text-overflow: ellipsis;
   white-space: nowrap;
   width: 214px;
 }
 
 .small-pod.extra-small .small-pod-name {
   left: 76px;
   padding: 16px 0;
   width: 190px;
 }
 
 @keyframes switch-image {
   from { transform: rotate3d(0, 1, 0, 90deg); }
   to { transform: none; }
 }