MD Settings: Fix scrolling bugs and hacks caused by undefined load behavior

chrome/browser/resources/settings/settings_page/main_page_behavior.js

 // Copyright 2016 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.
 
 /**
- * Calls |readyTest| repeatedly until it returns true, then calls
- * |readyCallback|.
- * @param {function():boolean} readyTest
- * @param {!Function} readyCallback
- */
-function doWhenReady(readyTest, readyCallback) {
-  if (readyTest()) {
-    readyCallback();
-    return;
-  }
-
-  // TODO(michaelpg): Remove this hack.
-  // See also: https://github.com/Polymer/polymer/issues/3629
-  var intervalId = setInterval(function() {
-    if (readyTest()) {
-      clearInterval(intervalId);
-      readyCallback();
-    }
-  }, 10);
-}
-
-/**
  * Responds to route changes by expanding, collapsing, or scrolling to sections
  * on the page. Expanded sections take up the full height of the container. At
  * most one section should be expanded at any given time.
  * @polymerBehavior MainPageBehavior
  */
 var MainPageBehaviorImpl = {
-  properties: {
-    // Name of the root route corresponding to this page.
-    route: String,
-  },
-
   /** @type {?HTMLElement} The scrolling container. */
   scroller: null,
 
   /** @override */
   attached: function() {
     if (this.domHost && this.domHost.parentNode.tagName == 'PAPER-HEADER-PANEL')
       this.scroller = this.domHost.parentNode.scroller;
     else
       this.scroller = document.body; // Used in unit tests.
   },
 
   /**
    * @param {!settings.Route} newRoute
    * @param {settings.Route} oldRoute
    */
   currentRouteChanged: function(newRoute, oldRoute) {
-    // Allow the page to load before expanding the section. TODO(michaelpg):
-    // Time this better when refactoring settings-animated-pages.
-    if (!oldRoute && newRoute.isSubpage()) {
+    // If this is the first route, or the page was hidden, allow the page to
+    // render before expanding the section.
+    if (!oldRoute && newRoute.contains(settings.getCurrentRoute()) ||
+        this.scrollHeight == 0) {
       setTimeout(this.tryTransitionToSection_.bind(this));
     } else {
-      doWhenReady(
-        function() {
-          return this.scrollHeight > 0 ||
-              !settings.Route[this.route].contains(settings.getCurrentRoute());
-        }.bind(this),
-        this.tryTransitionToSection_.bind(this));
+      this.tryTransitionToSection_();
     }
   },
 
   /**
    * If possible, transitions to the current route's section (by expanding or
    * scrolling to it). If another transition is running, finishes or cancels
    * that one, then schedules this function again. This ensures the current
    * section is quickly shown, without getting the page into a broken state --
    * if currentRoute changes in between calls, just transition to the new route.
    * @private
@@ skipping 214 matching lines @@
     return /** @type {?SettingsSectionElement} */(
         this.$$('settings-section[section="' + section + '"]'));
   },
 };
 
 /** @polymerBehavior */
 var MainPageBehavior = [
   settings.RouteObserverBehavior,
   MainPageBehaviorImpl,
 ];