settings: Keep focus on lock screen password prompt after wrong password.

Test: browser_tests CrSettingsPeoplePageQuickUnlockAuthenticateTest.*
Bug: 786930
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I658551a326421e94933b071ddc218979b7d8de86
Reviewed-on: https://chromium-review.googlesource.com/792096Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519799}

chrome/browser/resources/settings/people_page/password_prompt_dialog.js

@@ -136,6 +136,12 @@ Polymer({
       // The password might have been cleared during the duration of the
       // getActiveModes call.
       this.passwordInvalid_ = !valid && !!this.password_;
+      // Return focus to the password input if it lost focus while being checked
+      // (user pressed confirm button).
+      if (this.passwordInvalid_ &&
+          this.shadowRoot.activeElement != this.$.passwordInput) {
+        this.$.passwordInput.focus();
+      }
 
       if (valid) {
         // Create the |this.setModes| closure and automatically clear it after

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

@@ -90,6 +90,16 @@ cr.define('settings_people_page_quick_unlock', function() {
         assertDeepEquals([''], quickUnlockPrivateApi.credentials);
       });
 
+      test('TapConfirmButtonWithWrongPasswordRestoresFocus', function() {
+        var confirmButton = getFromElement('#passwordInput');
+        quickUnlockPrivateApi.accountPassword = 'bar';
+        passwordElement.value = 'foo';
+        MockInteractions.tap(
+            getFromElement('paper-button[class="action-button"]'));
+
+        assertEquals(element.shadowRoot.activeElement, passwordElement);
+      });
+
       // A bad password does not provide an authenticated setModes object, and a
       // entered password correctly uma should not be recorded.
       test('InvalidPasswordDoesNotProvideAuthentication', function() {