MD Downloads: limit the amount of downloads we send

chrome/browser/resources/md_downloads/manager.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.
 
 cr.define('downloads', function() {
   var Manager = Polymer({
     is: 'downloads-manager',
 
     properties: {
       hasDownloads_: {
         observer: 'hasDownloadsChanged_',
         type: Boolean,
       },
 
       items_: {
         type: Array,
         value: function() { return []; },
       },
     },
 
     hostAttributes: {
       loading: true,
     },
 
+    listeners: {
+      'downloads-list.scroll': 'onListScroll_',
+    },
+
     observers: [
       'itemsChanged_(items_.*)',
     ],
 
     /** @private */
     clearAll_: function() {
       this.set('items_', []);
     },
 
     /** @private */
@@ skipping 47 matching lines @@
      * @param {Event} e
      * @private
      */
     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();
     },
 
+    /**
+     * @param {Event} e
+     * @private
+     */
+    onListScroll_: function(e) {
+      var list = this.$['downloads-list'];
+      if (list.scrollHeight - list.scrollTop - list.offsetHeight <= 100) {
+        // Approaching the end of the scrollback. Attempt to load more items.
+        downloads.ActionService.getInstance().loadMore();
+      }
+    },
+
     /** @private */
     onLoad_: function() {
       cr.ui.decorate('command', cr.ui.Command);
       document.addEventListener('canExecute', this.onCanExecute_.bind(this));
       document.addEventListener('command', this.onCommand_.bind(this));
 
-      // Shows all downloads.
-      downloads.ActionService.getInstance().search('');
+      downloads.ActionService.getInstance().loadMore();
     },
 
     /**
      * @param {number} index
      * @private
      */
     removeItem_: function(index) {
       this.splice('items_', index, 1);
       this.updateHideDates_(index, index);
+      this.onListScroll_();
     },
 
     /**
      * @param {number} start
      * @param {number} end
      * @private
      */
     updateHideDates_: function(start, end) {
       for (var i = start; i <= end; ++i) {
         var current = this.items_[i];
@@ skipping 37 matching lines @@
   Manager.removeItem = function(index) {
     Manager.get().removeItem_(index);
   };
 
   Manager.updateItem = function(index, data) {
     Manager.get().updateItem_(index, data);
   };
 
   return {Manager: Manager};
 });