Chrome OS: Update color of option subtitles in OOBE Advanced Options.

Bug: 900413
Change-Id: I58da79246fb029656af59877b43b9743e893d3d0
Reviewed-on: https://chromium-review.googlesource.com/c/1311654Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604444}

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

@@ -74,6 +74,6 @@
 }
 
 #oobeAdvancedOptionsScreen .advanced-option-subtitle {
-  color: var(--google-grey-900);
+  color: var(--google-grey-refresh-700); /* #5F6368 */
   font-size: 13px;
 }

chrome/browser/resources/chromeos/login/oobe_welcome.html

@@ -2,6 +2,7 @@
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
+<link rel="import" href="chrome://resources/cr_elements/shared_vars_css.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-iconset-svg/iron-iconset-svg.html">