MD Downloads: add "waterfall" shadow (shows when the list is scrolled)

chrome/browser/resources/md_downloads/crisper.js

 // Copyright (c) 2013 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.
 function assert(condition, opt_message) {
   if (!condition) {
     var message = 'Assertion failed';
     if (opt_message) message = message + ': ' + opt_message;
     var error = new Error(message);
     var global = function() {
       return this;
@@ skipping 6849 matching lines @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 cr.define('downloads', function() {
   var Manager = Polymer({
     is: 'downloads-manager',
     properties: {
       hasDownloads_: {
         observer: 'hasDownloadsChanged_',
         type: Boolean
       },
+      hasShadow_: {
+        type: Boolean,
+        value: false,
+        reflectToAttribute: true
+      },
       items_: {
         type: Array,
         value: function() {
           return [];
         }
       },
       spinnerActive_: {
         type: Boolean,
         notify: true
       }
@@ skipping 44 matching lines @@
       }
     },
     onCommand_: function(e) {
       if (e.command.id == 'clear-all-command') downloads.ActionService.getInstance().clearAll(); else if (e.command.id == 'undo-command') downloads.ActionService.getInstance().undo(); else if (e.command.id == 'find-command') this.$.toolbar.onFindCommand();
     },
     onListScroll_: function() {
       var list = this.$['downloads-list'];
       if (list.scrollHeight - list.scrollTop - list.offsetHeight <= 100) {
         downloads.ActionService.getInstance().loadMore();
       }
+      this.hasShadow_ = list.scrollTop > 0;
     },
     onLoad_: function() {
       cr.ui.decorate('command', cr.ui.Command);
       document.addEventListener('canExecute', this.onCanExecute_.bind(this));
       document.addEventListener('command', this.onCommand_.bind(this));
       downloads.ActionService.getInstance().loadMore();
     },
     removeItem_: function(index) {
       this.splice('items_', index, 1);
       this.updateHideDates_(index, index);
@@ skipping 34 matching lines @@
   };
   return {
     Manager: Manager
   };
 });
 
 // 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.
 window.addEventListener('load', downloads.Manager.onLoad);