[MD settings] shrink overscroll when scrolling up

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.
 
 /**
  * @fileoverview
  * 'settings-main' displays the selected settings page.
  */
 Polymer({
   is: 'settings-main',
@@ skipping 53 matching lines @@
     /**
      * Dictionary defining page visibility.
      * @type {!GuestModePageVisibility}
      */
     pageVisibility: {
       type: Object,
       value: function() { return {}; },
     },
   },
 
+  /**
+   * The smallest value for the height of the overscroll padding.
+   * @const {number}
+   */
+  MINIMUM_OVERSCROLL: 64,

[Dan Beam, 2016/08/02 21:57:36]

can you make this private?

[dschuyler, 2016/08/02 22:32:44]

Done. And then ended up removing it.

+
   /** @override */
   attached: function() {
     document.addEventListener('toggle-advanced-page', function(e) {
       this.advancedToggleExpanded_ = e.detail;
       settings.navigateTo(this.advancedToggleExpanded_ ?
           settings.Route.ADVANCED : settings.Route.BASIC);
     }.bind(this));
+
+    var mainContainer = this.domHost.$$('paper-header-panel').$.mainContainer;
+    mainContainer.addEventListener('scroll', function() {
+      let visibleBottom = mainContainer.scrollTop + mainContainer.clientHeight;
+      let overscrollBottom = this.$.overscroll.offsetTop +

[Dan Beam, 2016/08/02 21:57:36]

nit: var overscroll = this.$.overscroll; (and re-use)

[dschuyler, 2016/08/02 22:32:44]

Done.

+          this.$.overscroll.scrollHeight;
+      // How much of the overscroll is visible (may be negative).
+      let visibleOverscroll = this.$.overscroll.scrollHeight -
+                     (overscrollBottom - visibleBottom);

[Dan Beam, 2016/08/02 21:57:36]

indent off

[dschuyler, 2016/08/02 22:32:44]

Done.

+      if (visibleOverscroll > this.MINIMUM_OVERSCROLL)
+        this.$.overscroll.style.paddingBottom = visibleOverscroll + 'px';
+    }.bind(this));
   },
 
   /**
    * @param {boolean} opened Whether the menu is expanded.
    * @return {string} Which icon to use.
    * @private
    */
   arrowState_: function(opened) {
     return opened ? 'settings:arrow-drop-up' : 'cr:arrow-drop-down';
   },
@@ skipping 30 matching lines @@
             this.pageVisibility.advancedSettings !== false);
         this.advancedToggleExpanded_ = true;
       }
     }
 
     // Wait for any other changes prior to calculating the overflow padding.
     setTimeout(function() {
       // Ensure any dom-if reflects the current properties.
       Polymer.dom.flush();
 
-      this.$.overscroll.style.paddingBottom = this.overscrollHeight_() + 'px';
+      this.$.overscroll.style.paddingBottom = Math.max(this.MINIMUM_OVERSCROLL,
+          this.overscrollHeight_()) + 'px';
     }.bind(this));
   },
 
   /**
    * Return the height that the overscroll padding should be set to.
    * This is used to determine how much padding to apply to the end of the
    * content so that the last element may align with the top of the content
    * area.
    * @return {number}
    * @private
@@ skipping 66 matching lines @@
 
   /**
    * @param {(boolean|undefined)} visibility
    * @return {boolean} True unless visibility is false.
    * @private
    */
   showAdvancedSettings_: function(visibility) {
     return visibility !== false;
   },
 });