[SplitSettings] Call correct function to open Release Notes

- Corrects the About page to calling the correct method on the
AboutPageBrowserProxy.
- Adds a test

Bug: 997155
Change-Id: If39b45274f6d3836b52039c22086b300b5d3f5b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1769625Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690139}

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

@@ -253,7 +253,7 @@ Polymer({
 
   /** @private */
   onReleaseNotesTap_: function() {
-    this.aboutBrowserProxy_.showReleaseNotes();
+    this.aboutBrowserProxy_.launchReleaseNotes();
   },
 
   /** @private */

chrome/test/data/webui/settings/chromeos/os_about_page_tests.js

@@ -347,6 +347,9 @@ cr.define('settings_about_page', function() {
         await initNewPage();
         await checkReleaseNotesOnline(true);
         await checkReleaseNotesOffline(false);
+
+        page.$$('#releaseNotesOnline').click();
+        return aboutBrowserProxy.whenCalled('launchReleaseNotes');
       });
 
       test('RegulatoryInfo', async () => {

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

@@ -16,8 +16,8 @@ class TestAboutPageBrowserProxy extends TestBrowserProxy {
       methodNames.push(
           'getChannelInfo', 'getVersionInfo', 'getRegulatoryInfo',
           'checkInternetConnection', 'getEnabledReleaseNotes',
-          'getHasEndOfLife', 'openOsHelpPage', 'refreshTPMFirmwareUpdateStatus',
-          'setChannel');
+          'getHasEndOfLife', 'launchReleaseNotes', 'openOsHelpPage',
+          'refreshTPMFirmwareUpdateStatus', 'setChannel');
     }
 
     if (cr.isMac) {
@@ -207,4 +207,9 @@ if (cr.isChromeOS) {
   TestAboutPageBrowserProxy.prototype.openOsHelpPage = function() {
     this.methodCalled('openOsHelpPage');
   };
+
+  /** @override */
+  TestAboutPageBrowserProxy.prototype.launchReleaseNotes = function() {
+    this.methodCalled('launchReleaseNotes');
+  };
 }