[ChromeOS] Use oauth's segmented spinner for sign-in loading UI.

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

+/* Copyright (c) 2011 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.
+ */
+
+@-webkit-keyframes spinner {
+  /* There are 13 animation steps, the numbers below space them evenly. Note
+   * that a steps(13) declaration produces off-by-one offsets for some frames,
+   * so for best results we specify positions explicity and use step-end. */
+  0%           { background-position: 286px 0px; }
+  7.6923076%   { background-position: 264px 0px; }
+  15.3846153%  { background-position: 242px 0px; }
+  23.0769230%  { background-position: 220px 0px; }
+  30.7692307%  { background-position: 198px 0px; }
+  38.4615384%  { background-position: 176px 0px; }
+  46.1538461%  { background-position: 154px 0px; }
+  53.8461538%  { background-position: 132px 0px; }
+  61.5384615%  { background-position: 110px 0px; }
+  69.2307692%  { background-position: 88px  0px; }
+  76.9230769%  { background-position: 66px  0px; }
+  84.6153846%  { background-position: 44px  0px; }
+  92.3076923%  { background-position: 22px  0px; }
+  100.0000000% { background-position: 0px   0px; }
+}
+
+.spinner {
+  -webkit-animation: spinner 1s step-end infinite;
+  background-image: url('chrome://theme/IDR_SPINNER');
+  height: 22px;
+  width: 22px;
+}