cros: Port SAML support to webview sign-in.

chrome/browser/resources/gaia_auth_host/webview_saml_injected.js

+// Copyright 2015 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.
+
+'use strict';
+
+/**
+ * Global injection guard that starts as undefined and sets to true after the
+ * first run. This is for webview.executeScript injection where the execution
+ * environment remains the same for multiple injections.
+ * @type {boolean}
+ */
+var samlInjectedInitialized;
+
+(function() {
+  if (samlInjectedInitialized)
+    return;
+  samlInjectedInitialized = true;
+
+  <include src="post_message_channel.js">
+  <include src="../gaia_auth/saml_injected.js">
+})();