New UI language should be first accept language.

When choosing a new UI language, enable it and put it at the top of the accept languages list.
That way the accept languages list reflects the user's language preferences.

Bug: 972033
Change-Id: I5bbee2f569f3a0d5941ebb161bcae751b3c41001
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1665650
Commit-Queue: Alexandre Frechette <frechette@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673367}

chrome/browser/resources/settings/chromeos/os_languages_page/os_languages_page.js

@@ -306,6 +306,8 @@ Polymer({
     this.isChangeInProgress_ = true;
     this.languageHelper.setProspectiveUILanguage(
         this.detailLanguage_.language.code);
+    this.languageHelper.moveLanguageToFront(this.detailLanguage_.language.code);
+
     this.closeMenuSoon_();
   },
 

chrome/browser/resources/settings/languages_page/languages_page.js

@@ -400,6 +400,8 @@ Polymer({
     this.isChangeInProgress_ = true;
     this.languageHelper.setProspectiveUILanguage(
         this.detailLanguage_.language.code);
+    this.languageHelper.moveLanguageToFront(this.detailLanguage_.language.code);
+
     this.closeMenuSoon_();
   },
   // </if>

chrome/test/data/webui/settings/languages_page_tests.js

@@ -395,8 +395,14 @@ cr.define('languages_page_tests', function() {
 
         return new Promise(resolve => {
           actionMenu.addEventListener('close', () => {
-            // Restart button is attached to 'sw' list item and is active.
-            assertTrue(!!swListItem.querySelector('#restartButton'));
+            // Restart button is attached to the first list item and is active.
+            const firstListItem =
+                languagesCollapse.querySelectorAll('.list-item')[0];
+            const domRepeat = languagesCollapse.querySelector('dom-repeat');
+            assertTrue(
+                domRepeat.modelForElement(firstListItem).item.language.code ==
+                'sw');
+            assertTrue(!!firstListItem.querySelector('#restartButton'));
             assertRestartButtonActiveState(true);
             resolve();
           });