[MD settings] shrink overscroll when scrolling up

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="/route.html">
 <link rel="import" href="/settings_page/main_page_behavior.html">
 <link rel="import" href="/settings_vars_css.html">
 
 <dom-module id="settings-main">
   <template>
     <style>
       #advancedToggle {
         @apply(--settings-actionable);
         align-items: center;
         display: flex;
-        margin-bottom: 24px;
+        margin-bottom: 3px;
         margin-top: 12px;  /* Part of a 48px spacer (33px + 12px + 3px). */
         min-height: 32px;
         padding: 0 12px;
       }
 
+      #overscroll {
+        margin-top: 64px;
+      }
+
       #toggleContainer {
         align-items: center;
         display: flex;
         justify-content: center;
-        margin-bottom: -var(--settings-page-vertical-margin);
       }
 
       #toggleSpacer {
         padding-top: 33px;  /* Part of a 48px spacer (33px + 12px + 3px). */
       }
 
       iron-icon {
         -webkit-margin-start: 16px;
       }
 
@@ skipping 35 matching lines @@
         <settings-advanced-page prefs="{{prefs}}"
             current-route="{{currentRoute}}"
             page-visibility="[[pageVisibility]]">
         </settings-advanced-page>
       </template>
     </template>
     <template is="dom-if" if="[[showPages_.about]]">
       <settings-about-page current-route="{{currentRoute}}">
       </settings-about-page>
     </template>
     <div id="overscroll"></div>

[Dan Beam, 2016/08/03 20:57:39]

properties: {
  overscroll_: {
    type: Number,
    observer: 'overscrollChanged_'
  },
}

/** @private */
overscrollChanged_: function() {
  if (!this.overscroll_ && this.boundScroll_) {
    this.parentNode.scroller.removeEventListener('scroll', this.boundScroll_)
    this.boundScroll_ = null;
  } else if (this.overscroll_ && !this.boundScroll_) {
    this.boundScroll_ = this.onScroll_.bind(this);
    this.parentNode.scroller.addEventListener('scroll', this.boundScroll_);
  }
},

/** @private */
onScroll_: function() {
  // the calcs
  this.overscroll_ = ...;  // NB: 10 rather than '10px'
},

and in the HTML:

  <div id="overscroll" style="padding-bottom: [[overscroll]]px"></div>
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[dschuyler, 2016/08/03 21:46:41]

Done.

   </template>
   <script src="settings_main.js"></script>
   <script src="/search_settings.js"></script>
 </dom-module>