Add JS type checking for c/b/r/signin/sigin_email_confirmation/.

This is in preparation of porting to Polymer3

Bug: 1012533
Change-Id: If15a48c57bc28a014c548d6d8e8136fdce462080
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881989Reviewed-by: Dan Beam <dbeam@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709734}

chrome/browser/resources/BUILD.gn

@@ -34,7 +34,7 @@ if (closure_compile) {
         "print_preview:closure_compile",
         "quota_internals:closure_compile",
         "settings:closure_compile",
-        "signin/sync_confirmation:closure_compile",
+        "signin:closure_compile",
         "usb_internals:closure_compile",
         "user_manager:closure_compile",
         "welcome:closure_compile",

chrome/browser/resources/signin/BUILD.gn

@@ -4,6 +4,13 @@
 
 import("//tools/polymer/polymer.gni")
 
+group("closure_compile") {
+  deps = [
+    "signin_email_confirmation:closure_compile",
+    "sync_confirmation:closure_compile",
+  ]
+}
+
 group("polymer3_elements") {
   deps = [
     ":signin_shared_css_module",

chrome/browser/resources/signin/signin_email_confirmation/BUILD.gn

+# Copyright 2019 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.
+
+import("//third_party/closure_compiler/compile_js.gni")
+
+js_type_check("closure_compile") {
+  deps = [
+    ":signin_email_confirmation",
+  ]
+}
+
+js_library("signin_email_confirmation") {
+  deps = [
+    "//ui/webui/resources/js:cr",
+    "//ui/webui/resources/js:load_time_data",
+    "//ui/webui/resources/js:util",
+  ]
+}

chrome/browser/resources/signin/signin_email_confirmation/signin_email_confirmation.js

@@ -6,9 +6,9 @@ cr.define('signin.emailConfirmation', function() {
   'use strict';
 
   function initialize() {
-    const args = JSON.parse(chrome.getVariableValue('dialogArguments'));
-    const lastEmail = args.lastEmail;
-    const newEmail = args.newEmail;
+    const args = /** @type {{lastEmail: string, newEmail: string}} */
+        (JSON.parse(chrome.getVariableValue('dialogArguments')));
+    const {lastEmail, newEmail} = args;
     $('dialogTitle').textContent =
         loadTimeData.getStringF('signinEmailConfirmationTitle', lastEmail);
     $('createNewUserRadioButtonSubtitle').textContent = loadTimeData.getStringF(