MD Downloads: add first meaningful paint metrics to UMA

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: {
       /** @private */
@@ skipping 34 matching lines @@
 
     listeners: {
       'downloads-list.scroll': 'onListScroll_',
       'toolbar.search-changed': 'onSearchChanged_',
     },
 
     observers: [
       'itemsChanged_(items_.*)',
     ],
 
+    /** @private {!PromiseResolver} */
+    loaded_: new PromiseResolver,
+
     /** @private */
     clearAll_: function() {
       this.set('items_', []);
     },
 
     /** @private */
     hasDownloadsChanged_: function() {
       if (loadTimeData.getBoolean('allowDeletingHistory'))
         this.$.toolbar.downloadsShowing = this.hasDownloads_;
 
       if (this.hasDownloads_)
         this.$['downloads-list'].fire('iron-resize');
     },
 
     /**
      * @param {number} index
      * @param {!Array<!downloads.Data>} list
      * @private
      */
     insertItems_: function(index, list) {
       this.splice.apply(this, ['items_', index, 0].concat(list));
       this.updateHideDates_(index, index + list.length);
-      this.removeAttribute('loading');
+
+      if (this.hasAttribute('loading')) {
+        this.removeAttribute('loading');
+        this.loaded_.resolve();
+      }
+
       this.spinnerActive_ = false;
     },
 
     /** @private */
     itemsChanged_: function() {
       this.hasDownloads_ = this.items_.length > 0;
     },
 
     /**
      * @return {string} The text to show when no download items are showing.
@@ skipping 39 matching lines @@
     /** @private */
     onListScroll_: function() {
       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();
       }
       this.hasShadow_ = list.scrollTop > 0;
     },
 
-    /** @private */
+    /**
+     * @return {!Promise}
+     * @private
+     */
     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();
+      return this.loaded_.promise;
     },
 
     /** @private */
     onSearchChanged_: function() {
       this.inSearchMode_ = downloads.ActionService.getInstance().isSearching();
     },
 
     /**
      * @param {number} index
      * @private
@@ skipping 40 matching lines @@
   /** @return {!downloads.Manager} */
   Manager.get = function() {
     return /** @type {!downloads.Manager} */(
         queryRequiredElement('downloads-manager'));
   };
 
   Manager.insertItems = function(index, list) {
     Manager.get().insertItems_(index, list);
   };
 
+  /** @return {!Promise} */
   Manager.onLoad = function() {
-    Manager.get().onLoad_();
+    return Manager.get().onLoad_();
   };
 
   Manager.removeItem = function(index) {
     Manager.get().removeItem_(index);
   };
 
   Manager.updateItem = function(index, data) {
     Manager.get().updateItem_(index, data);
   };
 
   return {Manager: Manager};
 });