settings ui: a11y improvement to security key fingerprint enrollment

Changes the fingeprint enrollment dialog on the security keys settings
subpage to iron-announce upon successful completion of a fingerprint
enrollment.

Bug: 974046
Change-Id: I61e4fc17d55bd16d2de299084586ec078829acc7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1898433Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#712639}

chrome/browser/resources/settings/privacy_page/BUILD.gn

@@ -110,6 +110,7 @@ js_library("security_keys_bio_enroll_dialog") {
   deps = [
     ":security_keys_browser_proxy",
     ":security_keys_pin_field",
+    "//third_party/polymer/v1_0/components-chromium/iron-a11y-announcer:iron-a11y-announcer-extracted",
     "//ui/webui/resources/cr_elements/cr_fingerprint:cr_fingerprint_progress_arc",
     "//ui/webui/resources/js:i18n_behavior",
   ]

chrome/browser/resources/settings/privacy_page/security_keys_bio_enroll_dialog.html

@@ -6,6 +6,7 @@
 <link rel="import" href="chrome://resources/cr_elements/cr_fingerprint/cr_fingerprint_progress_arc.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_icon_button/cr_icon_button.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
+<link rel="import" href="chrome://resources/polymer/v1_0/iron-a11y-announcer/iron-a11y-announcer.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-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-pages/iron-pages.html">

chrome/browser/resources/settings/privacy_page/security_keys_bio_enroll_dialog.js

@@ -71,6 +71,10 @@ Polymer({
 
   /** @override */
   attached: function() {
+    Polymer.RenderStatus.afterNextRender(this, function() {
+      Polymer.IronA11yAnnouncer.requestAvailability();
+    });
+
     this.$.dialog.showModal();
     this.addWebUIListener(
         'security-keys-bio-enroll-error', this.onError_.bind(this));
@@ -224,6 +228,8 @@ Polymer({
       this.progressArcLabel_ =
           this.i18n('securityKeysBioEnrollmentEnrollingCompleteLabel');
       this.$.confirmButton.focus();
+      // Make screen-readers announce enrollment completion.
+      this.fire('iron-announce', {text: this.progressArcLabel_});
     }
     this.fire('bio-enroll-dialog-ready-for-testing');
   },