Fire an error if a pref used in the UI is missing once all prefs are fetched.

BUG=469919

Review URL: https://codereview.chromium.org/1029743002

Cr-Commit-Position: refs/heads/master@{#322120}

chrome/browser/resources/settings/a11y_page/a11y_page.css

@@ -17,3 +17,7 @@
   margin: 0;
   padding: 0 0 0.25em;
 }
+
+.more-a11y-link {
+  margin-bottom: 10px;
+}

chrome/browser/resources/settings/a11y_page/a11y_page.html

@@ -13,6 +13,14 @@
     <paper-shadow layout vertical cross-fade>
       <cr-settings-page-header page="{{}}"></cr-settings-page-header>
 
+      <div class="more-a11y-link">
+        <a href="https://chrome.google.com/webstore/category/collection/accessibility"
+            target="_blank">
+          Add additional accessibility features
+        </a>
+      </div>
+
+<if expr="chromeos">
       <cr-settings-checkbox pref="{{prefs.settings.a11y.enable_menu}}"
           label="Show accessibility options in the system menu">
       </cr-settings-checkbox>
@@ -53,6 +61,8 @@
 
       <cr-settings-checkbox pref="{{prefs.settings.a11y.virtual_keyboard}}"
           label="Enable on-screen keyboard"></cr-settings-checkbox>
+</if>
+
     </paper-shadow>
   </template>
   <script src="a11y_page.js"></script>

chrome/browser/resources/settings/checkbox/checkbox.html

 <link rel="import" href="chrome://resources/polymer/core-label/core-label.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_checkbox/cr_checkbox.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_events/cr_events.html">
+<link rel="import" href="chrome://md-settings/pref_tracker/pref_tracker.html">
 
 <polymer-element name="cr-settings-checkbox">
   <template>
     <link rel="stylesheet" href="checkbox.css">
     <cr-events id="events"></cr-events>
+    <cr-settings-pref-tracker pref="{{pref}}"></cr-settings-pref-tracker>
+
     <core-label horizontal layout>
       <cr-checkbox id="checkbox" checked="{{pref.value}}"
           disabled="{{pref.disabled}}" for></cr-checkbox>

chrome/browser/resources/settings/pref_tracker/pref_tracker.html

+<link rel="import" href="chrome://resources/polymer/polymer/polymer.html">
+
+<polymer-element name="cr-settings-pref-tracker">
+  <script src="chrome://md-settings/prefs/prefs_types.js"></script>
+  <script src="pref_tracker.js"></script>
+</polymer-element>

chrome/browser/resources/settings/pref_tracker/pref_tracker.js

+// Copyright 2015 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.
+
+/**
+ * @fileoverview
+ * `cr-settings-pref-tracker` is a utility element used to track the
+ * initialization of a specified preference and throw an error if the pref
+ * is not defined after prefs have all been fetched.
+ *
+ * Example:
+ *
+ *    <cr-settings-pref-tracker pref="{{prefs.settings.foo.bar}}">
+ *    </cr-settings-pref-tracker>
+ *
+ * @element cr-settings-pref-tracker
+ */
+(function() {
+
+  /**
+   * An array of all the tracker instances.
+   * @type {!Array<!CrSettingsPrefTrackerElement>}
+   */
+  var instances = [];
+
+  /**
+   * Validates all tracker instances.
+   * @private
+   */
+  var validateAll_ = function() {
+    instances.forEach(function(tracker) {
+      tracker.validate_();
+    });
+  };
+
+  document.addEventListener(CrSettingsPrefs.INITIALIZED, validateAll_);
+
+  Polymer('cr-settings-pref-tracker', {
+    publish: {
+      /**
+       * The Preference object being tracked.
+       *
+       * @attribute pref
+       * @type {Object}
+       * @default null
+       */
+      pref: null,
+    },
+
+    observe: {
+      pref: 'validate_',
+    },
+
+    /** @override */
+    ready: function() {
+      this.validate_();
+
+      instances.push(this);
+    },
+
+    /**
+     * Throws an error if prefs are initialized and the tracked pref is not
+     * found.
+     * @private
+     */
+    validate_: function() {
+      this.async(function() {
+        // Note that null == undefined.
+        if (CrSettingsPrefs.isInitialized && this.pref == null) {
+          // HACK ALERT: This is the best clue we have as to the pref key for
+          // this tracker. This value should not be relied upon anywhere or
+          // actually used besides for this error message.
+          var keyHint = '';
+          var parentPrefString = this.parentNode && this.parentNode.host &&
+              this.parentNode.host.getAttribute('pref');
+          if (parentPrefString) {
+            keyHint = parentPrefString.match(/{{([a-z._]+)}}/)[1];
+          }
+
+          throw new Error('Pref not found. Key Hint: ' + keyHint);
+        }
+      });
+    },
+  });
+})();

chrome/browser/resources/settings/prefs/prefs.html

@@ -3,5 +3,6 @@
 <link rel="import" href="chrome://resources/html/cr.html">
 
 <polymer-element name="cr-settings-prefs">
+  <script src="prefs_types.js"></script>
   <script src="prefs.js"></script>
 </polymer-element>

chrome/browser/resources/settings/prefs/prefs.js

@@ -57,7 +57,7 @@
        * Object containing all preferences.
        *
        * @attribute settings
-       * @type CrSettingsPrefs.Settings
+       * @type {Object}
        * @default null
        */
       settings: null,
@@ -65,6 +65,7 @@
 
     /** @override */
     created: function() {
+      CrSettingsPrefs.isInitialized = false;
       this.settings = {};
       this.fetchSettings_();
     },
@@ -94,6 +95,8 @@
      */
     onPrefsFetched_: function(dict) {
       this.parsePrefDict_('', dict);
+      CrSettingsPrefs.isInitialized = true;
+      document.dispatchEvent(new Event(CrSettingsPrefs.INITIALIZED));
     },
 
     /**

chrome/browser/resources/settings/prefs/prefs_types.js

@@ -3,46 +3,21 @@
 // found in the LICENSE file.
 
 /**
- * @fileoverview Typedefs for CrSettingsPrefsElement.
+ * @fileoverview Types for CrSettingsPrefsElement.
  */
 
-var CrSettingsPrefs = {};
+if (CrSettingsPrefs === undefined) {
+  var CrSettingsPrefs = {};
 
-/**
- * @typedef {{
- *   a11y: CrSettingsPrefs.A11y,
- *   touchpad: CrSettingsPrefs.Touchpad,
- *   downloads: CrSettingsPrefs.Downloads,
- *   accessibility: boolean
- * }}
- */
-CrSettingsPrefs.Settings;
-
-/**
- * @typedef {{
- *   enableMenu: boolean,
- *   largeCursorEnabled: boolean,
- *   highContrastEnabled: boolean,
- *   stickyKeysEnabled: boolean,
- *   screenMagnifier: boolean,
- *   autoclick: boolean,
- *   autoclickDelayMs: number,
- *   virtualKeyboard: boolean
- * }}
- */
-CrSettingsPrefs.A11y;
+  /**
+   * The type of the event fired when prefs have been fetched and initialized.
+   * @const {string}
+   */
+  CrSettingsPrefs.INITIALIZED = 'cr-settings-prefs-initialized';
 
-/**
- * @typedef {{
- *   downloadLocation: string,
- *   promptForDownload: boolean
- * }}
- */
-CrSettingsPrefs.Downloads;
-
-/**
- * @typedef {{
- *   enableTapDragging: boolean
- * }}
- */
-CrSettingsPrefs.Touchpad;
+  /**
+   * Global boolean set to true when all settings have been initialized.
+   * @type {boolean}
+   */
+  CrSettingsPrefs.isInitialized = false;
+}

chrome/browser/resources/settings/settings_resources.grd

@@ -17,7 +17,9 @@
                  type="chrome_html" />
       <structure name="IDR_SETTINGS_A11Y_PAGE_HTML"
                  file="a11y_page/a11y_page.html"
-                 type="chrome_html" />
+                 type="chrome_html"
+                 flattenhtml="true"
+                 allowexternalscript="true" />
       <structure name="IDR_SETTINGS_A11Y_PAGE_CSS"
                  file="a11y_page/a11y_page.css"
                  type="chrome_html" />
@@ -99,6 +101,15 @@
       <structure name="IDR_SETTINGS_PREFS_HTML"
                  file="prefs/prefs.html"
                  type="chrome_html" />
+      <structure name="IDR_SETTINGS_PREFS_TYPES_JS"
+                 file="prefs/prefs_types.js"
+                 type="chrome_html" />
+      <structure name="IDR_SETTINGS_PREF_TRACKER_HTML"
+                 file="pref_tracker/pref_tracker.html"
+                 type="chrome_html" />
+      <structure name="IDR_SETTINGS_PREF_TRACKER_JS"
+                 file="pref_tracker/pref_tracker.js"
+                 type="chrome_html" />
       <structure name="IDR_SETTINGS_SETTINGS_HTML"
                  file="settings.html"
                  type="chrome_html" />