Move settings-section animations into setting-section, make better

chrome/browser/resources/settings/settings_main/settings_main.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="/about_page/about_page.html">
 <link rel="import" href="/advanced_page/advanced_page.html">
 <link rel="import" href="/basic_page/basic_page.html">
 <link rel="import" href="/settings_page/main_page_behavior.html">
 <link rel="import" href="/settings_root_css.html">
 
 <dom-module id="settings-main">
@@ skipping 19 matching lines @@
       #toggleSpacer {
         padding-top: 33px;  /* Part of a 48px spacer (33px + 12px + 3px). */
       }
 
       iron-icon {
         -webkit-margin-start: 16px;
       }
     </style>
     <content select="paper-icon-button"></content>
     <template is="dom-if" if="[[showBasicPage_]]">
-      <settings-basic-page prefs="{{prefs}}" current-route="{{currentRoute}}">
+      <settings-basic-page prefs="{{prefs}}" current-route="{{currentRoute}}"
+          on-subpage-expand="subpageExpanded_"

[michaelpg, 2016/06/28 23:45:16]

dschuyler, please take a look at these changes. We can't have the advanced page
and the toggle button disappear when a section is clicked, because that (a)
looks weird and (b) shortens the page which can change the scroll height.

+          on-subpage-collapsing="subpageCollapsing_">
       </settings-basic-page>
     </template>
     <template is="dom-if" if="[[showAdvancedToggle_]]">
       <div id="toggleSpacer"></div>
       <div id="toggleContainer">
         <div id="advancedToggle" on-tap="toggleAdvancedPage_">
           <span>$i18n{advancedPageTitle}</span>
           <iron-icon icon="[[arrowState_(showAdvancedPage_)]]"></iron-icon>
         </div>
       </div>
     </template>
     <template is="dom-if" if="[[showAdvancedPage_]]">
       <settings-advanced-page prefs="{{prefs}}"
-          current-route="{{currentRoute}}">
+          current-route="{{currentRoute}}"
+          on-subpage-expand="subpageExpanded_"
+          on-subpage-collapsing="subpageCollapsing_">
       </settings-advanced-page>
     </template>
     <template is="dom-if" if="[[showAboutPage_]]">
       <settings-about-page current-route="{{currentRoute}}">
       </settings-about-page>
     </template>
   </template>
   <script src="settings_main.js"></script>
 </dom-module>