MD Settings: methods to get root pages and sections

chrome/browser/resources/settings/settings_main/settings_main.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.
 
 /**
  * @typedef {{about: boolean, basic: boolean, advanced: boolean}}
  */
 var MainPageVisibility;
 
 /**
@@ skipping 161 matching lines @@
    * content so that the last element may align with the top of the content
    * area.
    * @return {number}
    * @private
    */
   overscrollHeight_: function() {
     var route = settings.getCurrentRoute();
     if (route.isSubpage() || this.showPages_.about)
       return 0;
 
-    var query = 'settings-section[section="' + route.section + '"]';
-    var topSection = this.$$('settings-basic-page').$$(query);
-    if (!topSection && this.showPages_.advanced)
-      topSection = this.$$('settings-advanced-page').$$(query);
-
+    var page = this.getPage_(route);
+    var topSection = page && page.getSection(route.section);
     if (!topSection || !topSection.offsetParent)
       return 0;
 
     // Offset to the selected section (relative to the scrolling window).
     let sectionTop = topSection.offsetParent.offsetTop + topSection.offsetTop;
     // The height of the selected section and remaining content (sections).
     let heightOfShownSections = this.$.overscroll.offsetTop - sectionTop;
     return Math.max(0, this.parentNode.scrollHeight - heightOfShownSections);
   },
 
   /** @private */
   toggleAdvancedPage_: function() {
     this.fire('toggle-advanced-page', !this.advancedToggleExpanded_);
   },
 
   /**
+   * Returns the root page (if it exists) for a route.
+   * @param {!settings.Route} route
+   * @return {(?SettingsAboutPageElement|?SettingsAdvancedPageElement|
+   *           ?SettingsBasicPageElement)}
+   */
+  getPage_: function(route) {
+    if (settings.Route.ABOUT.contains(route)) {
+      return /** @type {?SettingsAboutPageElement} */(
+          this.$$('settings-about-page'));
+    }
+    if (settings.Route.ADVANCED.contains(route)) {
+      return /** @type {?SettingsAdvancedPageElement} */(
+          this.$$('settings-advanced-page'));
+    }
+    if (settings.Route.BASIC.contains(route)) {
+      return /** @type {?SettingsBasicPageElement} */(
+          this.$$('settings-basic-page'));
+    }
+    assertNotReached();
+  },
+
+  /**
    * Navigates to the default search page (if necessary).
    * @private
    */
   ensureInDefaultSearchPage_: function() {
     if (settings.getCurrentRoute() != settings.Route.BASIC)
       settings.navigateTo(settings.Route.BASIC);
   },
 
   /**
    * @param {string} query
    * @return {!Promise} A promise indicating that searching finished.
    */
   searchContents: function(query) {
     if (!this.previousShowPages_) {
       // Store which pages are shown before search, so that they can be restored
       // after the user clears the search results.
       this.previousShowPages_ = this.showPages_;
     }
 
     this.ensureInDefaultSearchPage_();
     this.toolbarSpinnerActive = true;
 
     // Trigger rendering of the basic and advanced pages and search once ready.
     this.showPages_ = {about: false, basic: true, advanced: true};
 
     return new Promise(function(resolve, reject) {
       setTimeout(function() {
         var whenSearchDone = settings.getSearchManager().search(
-            query, assert(this.$$('settings-basic-page')));
+            query, assert(this.getPage_(settings.Route.BASIC)));
         assert(
             whenSearchDone ===
                 settings.getSearchManager().search(
-                    query, assert(this.$$('settings-advanced-page'))));
+                    query, assert(this.getPage_(settings.Route.ADVANCED))));
 
         whenSearchDone.then(function(request) {
           resolve();
           if (!request.finished) {
             // Nothing to do here. A previous search request was canceled
             // because a new search request was issued before the first one
             // completed.
             return;
           }
 
@@ skipping 14 matching lines @@
 
   /**
    * @param {(boolean|undefined)} visibility
    * @return {boolean} True unless visibility is false.
    * @private
    */
   showAdvancedSettings_: function(visibility) {
     return visibility !== false;
   },
 });