Port downloads.ItemView to a Polymer component.

chrome/browser/resources/md_downloads/manager.js

Index: chrome/browser/resources/md_downloads/manager.js
diff --git a/chrome/browser/resources/md_downloads/manager.js b/chrome/browser/resources/md_downloads/manager.js
index 16caf24f01915b06f8b6d791fa21138699fbeb57..3371629e77ae747e1ddc371c61178af9d7a1e508 100644
--- a/chrome/browser/resources/md_downloads/manager.js
+++ b/chrome/browser/resources/md_downloads/manager.js
@@ -37,8 +37,57 @@ cr.define('downloads', function() {
      * @private
      */
     updateAll_: function(list) {
-      /** @private {!Array} */
-      this.items_ = list;
+      var oldIdMap = this.idMap_ || {};
+
+      /** @private {!Object<!downloads.ItemView>} */
+      this.idMap_ = {};
+
+      /** @private {!Array<!downloads.ItemView>} */
+      this.items_ = [];
+
+      for (var i = 0; i < list.length; ++i) {
+        var data = list[i];
+        var id = data.id;
+
+        // Re-use old items when possible (saves work, preserves focus).
+        var item = oldIdMap[id] || new downloads.ItemView;
+
+        this.idMap_[id] = item;  // Associated by ID for fast lookup.
+        this.items_.push(item);  // Add to sorted list for order.
+
+        // Render |item| but don't actually add to the DOM yet. |this.items_|
+        // must be fully created to be able to find the right spot to insert.
+        item.update(data);
+
+        // Collapse redundant dates.
+        var prev = list[i - 1];
+        item.dateContainer.hidden =
+            prev && prev.date_string == data.date_string;
+
+        delete oldIdMap[id];
+      }
+
+      // Remove stale, previously rendered items from the DOM.
+      for (var id in oldIdMap) {
+        if (oldIdMap[id].parentNode)
+          oldIdMap[id].parentNode.removeChild(oldIdMap[id]);
+        delete oldIdMap[id];
+      }
+
+      for (var i = 0; i < this.items_.length; ++i) {
+        var item = this.items_[i];
+        if (item.parentNode)  // Already in the DOM; skip.
+          continue;
+
+        var before = null;
+        // Find the next rendered item after this one, and insert before it.
+        for (var j = i + 1; !before && j < this.items_.length; ++j) {
+          if (this.items_[j].parentNode)
+            before = this.items_[j];
+        }
+        // If |before| is null, |item| will just get added at the end.
+        this.node_.insertBefore(item, before);
+      }
 
       var noDownloadsOrResults = $('no-downloads-or-results');
       noDownloadsOrResults.textContent = loadTimeData.getString(
@@ -53,6 +102,14 @@ cr.define('downloads', function() {
     },
 
     /**
+     * @param {!downloads.Data} data
+     * @private
+     */
+    updateItem_: function(data) {
+      this.idMap_[data.id].update(data);
+    },
+
+    /**
      * @return {number} The number of downloads shown on the page.
      * @private
      */
@@ -139,7 +196,9 @@ cr.define('downloads', function() {
     Manager.getInstance().updateAll_(list);
   };
 
-  Manager.updateItem = function(item) {};
+  Manager.updateItem = function(item) {
+    Manager.getInstance().updateItem_(item);
+  };
 
   Manager.setSearchText = function(searchText) {
     Manager.getInstance().setSearchText_(searchText);