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

chrome/browser/resources/options2/chromeos/change_picture_options.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. */
 
 #change-picture-page .content-area {
   min-width: 800px;
 }
 
 #user-image-grid {
   -webkit-user-drag: none;
@@ skipping 162 matching lines @@
   background: url('chrome://theme/IDR_USER_IMAGE_RECYCLE')
       no-repeat center 0;
   display: block;
 }
 
 [camera=webrtc] .camera.live.online #take-photo {
   background: url('chrome://theme/IDR_USER_IMAGE_CAPTURE')
       no-repeat center -1px;
   display: block;
 }
+
+#user-image-attribution {
+  -webkit-padding-start: 34px;
+  line-height: 26px;
+}
+
+#user-image-author-website {
+  -webkit-padding-start: 5px;
+}