MD Downloads: limit the amount of downloads we send

chrome/browser/resources/md_downloads/crisper.js

Index: chrome/browser/resources/md_downloads/crisper.js
diff --git a/chrome/browser/resources/md_downloads/crisper.js b/chrome/browser/resources/md_downloads/crisper.js
index ee13e9ccc5999ff5cc0467850c70ed2c6112fb24..15a1848f29225c7d757b89e221ee6d5adb1949bd 100644
--- a/chrome/browser/resources/md_downloads/crisper.js
+++ b/chrome/browser/resources/md_downloads/crisper.js
@@ -1578,15 +1578,17 @@ cr.define('downloads', function() {
     /** @param {string} id ID of the download that the user started dragging. */
     drag: chromeSendWithId('drag'),
 
-    /** @private {boolean} */
-    isSearching_: false,
+    /** Loads more downloads with the current search terms. */
+    loadMore: function() {
+      chrome.send('getDownloads', this.searchTerms_);
+    },
 
     /**
      * @return {boolean} Whether the user is currently searching for downloads
      *     (i.e. has a non-empty search term).
      */
     isSearching: function() {
-      return this.isSearching_;
+      return this.searchTerms_.length > 0;
     },
 
     /** Opens the current local destination for downloads. */
@@ -1618,12 +1620,15 @@ cr.define('downloads', function() {
         return;
 
       this.searchText_ = searchText;
+      this.searchTerms_ = ActionService.splitTerms(this.searchText_);
+      this.loadMore();
+    },
 
-      var terms = ActionService.splitTerms(searchText);
-      this.isSearching_ = terms.length > 0;
+    /** @private {Array<string>} */
+    searchTerms_: [],
 
-      chrome.send('getDownloads', terms);
-    },
+    /** @private {string} */
+    searchText_: '',
 
     /**
      * Shows the local folder a finished download resides in.
@@ -16976,6 +16981,10 @@ cr.define('downloads', function() {
       loading: true,
     },
 
+    listeners: {
+      'downloads-list.scroll': 'onListScroll_',
+    },
+
     observers: [
       'itemsChanged_(items_.*)',
     ],
@@ -17043,14 +17052,26 @@ cr.define('downloads', function() {
         downloads.ActionService.getInstance().undo();
     },
 
+    /**
+     * @param {Event} e
+     * @private
+     */
+    onListScroll_: function(e) {
+      var list = this.$['downloads-list'];
+      if (list.scrollHeight > list.offsetHeight &&
+          list.scrollTop + list.offsetHeight == list.scrollHeight) {
+        // Reached 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();
     },
 
     /**