settings: Disable lock screen password prompt button when no password.

Test: covered by tests
Bug: 838103
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I0bde97d3398ae60968d3646ee8254d24270c84df
Reviewed-on: https://chromium-review.googlesource.com/1056227Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559299}

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

@@ -29,6 +29,7 @@
             invalid$="[[passwordInvalid_]]"
             on-input="onPasswordChanged_"
             error-message="$i18n{passwordPromptInvalidPassword}"
+            on-value-changed="onValueChanged_"
             aria-disabled="false">
         </paper-input>
       </div>
@@ -37,8 +38,8 @@
           $i18n{cancel}
         </paper-button>
 
-        <paper-button class="action-button" on-click="submitPassword_"
-            disabled$="[[!enableConfirm_(password_, passwordInvalid_)]]">
+        <paper-button id="confirmButton" class="action-button"
+            disabled$="[[!confirmEnabled_]]" on-click="submitPassword_">
           $i18n{confirm}
         </paper-button>
       </div>

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

@@ -44,7 +44,7 @@ Polymer({
     },
 
     /**
-     * Authhentication token used when calling setModes, returned by
+     * Authentication token used when calling setModes, returned by
      * quickUnlockPrivate.getAuthToken. Reflected to lock-screen.
      * @private
      */
@@ -53,6 +53,13 @@ Polymer({
       notify: true,
     },
 
+    /**
+     * Helper property which marks whether the confirm button should be enabled
+     * or disabled.
+     * @private
+     */
+    confirmEnabled_: Boolean,
+
     /**
      * Helper property which marks password as valid/invalid.
      * @private
@@ -165,8 +172,8 @@ Polymer({
   },
 
   /** @private */
-  enableConfirm_: function() {
-    return !!this.$.passwordInput.value && !this.passwordInvalid_;
+  onValueChanged_: function() {
+    this.confirmEnabled_ = this.$.passwordInput.value && !this.passwordInvalid_;
   },
 });
 })();

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

@@ -164,6 +164,18 @@ cr.define('settings_people_page_quick_unlock', function() {
           done();
         }, 0);
       });
+
+      // Tests that he confirm button is diabled when there is nothing entered.
+      test('ConfirmButtonDisabled', function() {
+        let confirmButton = testElement.$$('#confirmButton');
+        assertTrue(!!confirmButton);
+        assertTrue(confirmButton.disabled);
+
+        passwordElement.value = 'foo';
+        assertFalse(!!confirmButton.disabled);
+        passwordElement.value = '';
+        assertTrue(confirmButton.disabled);
+      });
     });
   }