[cros] Add attribution (author & website) strings to stock user images.

chrome/browser/resources/chromeos/login/oobe.css

 /* 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.
  *
  * This is the stylesheet used by the Out of the box experience (OOBE) flow,
  * sign in and lock screens.
  */
 
 html,
 body {
@@ skipping 647 matching lines @@
 html[camera=webrtc] .camera.live.online #take-photo {
   background: url('chrome://theme/IDR_USER_IMAGE_CAPTURE')
       no-repeat center -1px;
   display: block;
 }
 
 #user-image-preview .perspective-box {
   -webkit-perspective: 600px;
 }
 
+#user-image-attribution {
+  /* Turned off for now. */
+  display: none;
+}
+
 /* TODO(nkostylev): Remove footer, button-strip styles. */
 #footer {
   height: 28px;  /* Same as button height */
 }
 
 #footer button {
   display: none;
   height: 28px;
 }
 
@@ skipping 583 matching lines @@
   width: 100%;
 }
 
 .background-initial {
   opacity: 0;
 }
 
 .background-final {
   opacity: 1;
 }