Revert of Revert "Typecheck JS files for chrome://extensions"

ui/webui/resources/js/cr/ui/list.js

Index: ui/webui/resources/js/cr/ui/list.js
diff --git a/ui/webui/resources/js/cr/ui/list.js b/ui/webui/resources/js/cr/ui/list.js
index 91df98de53466534e19737e5a41693d7f65864bd..4fc97ba510614ef5b39a9b931a7a5a0a7b74ed16 100644
--- a/ui/webui/resources/js/cr/ui/list.js
+++ b/ui/webui/resources/js/cr/ui/list.js
@@ -21,7 +21,7 @@
    * false if the mouseevent was generated over a border or a scrollbar.
    * @param {!HTMLElement} el The element to test the event with.
    * @param {!Event} e The mouse event.
-   * @param {boolean} Whether the mouse event was inside the viewport.
+   * @return {boolean} Whether the mouse event was inside the viewport.
    */
   function inViewport(el, e) {
     var rect = el.getBoundingClientRect();
@@ -53,11 +53,11 @@
      * is needed. Note that lead item is allowed to have a different height, to
      * accommodate lists where a single item at a time can be expanded to show
      * more detail.
-     * @type {{height: number, marginTop: number, marginBottom:number,
-     *     width: number, marginLeft: number, marginRight:number}}
-     * @private
-     */
-    measured_: undefined,
+     * @type {?{height: number, marginTop: number, marginBottom: number,
+     *     width: number, marginLeft: number, marginRight: number}}
+     * @private
+     */
+    measured_: null,
 
     /**
      * Whether or not the list is autoexpanding. If true, the list resizes
@@ -85,14 +85,14 @@
 
     /**
      * Function used to create grid items.
-     * @type {function(): !ListItem}
+     * @type {function(new:cr.ui.ListItem, Object)}
      * @private
      */
     itemConstructor_: cr.ui.ListItem,
 
     /**
      * Function used to create grid items.
-     * @type {function(): !ListItem}
+     * @return {function(new:cr.ui.ListItem, Object)}
      */
     get itemConstructor() {
       return this.itemConstructor_;
@@ -242,7 +242,7 @@
 
     /**
      * Convenience alias for selectionModel.selectedItems
-     * @type {!Array<*>}
+     * @type {!Array.<*>}
      */
     get selectedItems() {
       var indexes = this.selectionModel.selectedIndexes;
@@ -397,16 +397,18 @@
      * @param {ListItem=} opt_item The list item to use to do the measuring. If
      *     this is not provided an item will be created based on the first value
      *     in the model.
-     * @return {{height: number, marginTop: number, marginBottom:number,
-     *     width: number, marginLeft: number, marginRight:number}}
+     * @return {{height: number, marginTop: number, marginBottom: number,
+     *     width: number, marginLeft: number, marginRight: number}}
      *     The height and width of the item, taking
      *     margins into account, and the top, bottom, left and right margins
      *     themselves.
      */
     measureItem: function(opt_item) {
       var dataModel = this.dataModel;
-      if (!dataModel || !dataModel.length)
-        return 0;
+      if (!dataModel || !dataModel.length) {
+        return {height: 0, marginTop: 0, marginBottom: 0,
+                width: 0, marginLeft: 0, marginRight: 0};
+      }
       var item = opt_item || this.cachedMeasuredItem_ ||
           this.createItem(dataModel.item(0));
       if (!opt_item) {
@@ -462,11 +464,11 @@
       if (this.disabled)
         return;
 
-      var target = e.target;
-
-      target = this.getListItemAncestor(target);
-      if (target)
-        this.activateItemAtIndex(this.getIndexOfListItem(target));
+      var target = /** @type {HTMLElement} */(e.target);
+
+      var ancestor = this.getListItemAncestor(target);
+      if (ancestor)
+        this.activateItemAtIndex(this.getIndexOfListItem(ancestor));
     },
 
     /**
@@ -478,7 +480,7 @@
       if (this.disabled)
         return;
 
-      var target = e.target;
+      var target = /** @type {HTMLElement} */(e.target);
 
       // If the target was this element we need to make sure that the user did
       // not click on a border or a scrollbar.
@@ -521,26 +523,23 @@
      * Returns the list item element containing the given element, or null if
      * it doesn't belong to any list item element.
      * @param {HTMLElement} element The element.
-     * @return {ListItem} The list item containing |element|, or null.
+     * @return {HTMLLIElement} The list item containing |element|, or null.
      */
     getListItemAncestor: function(element) {
       var container = element;
       while (container && container.parentNode != this) {
         container = container.parentNode;
       }
-      return container;
+      return container && assertInstanceof(container, HTMLLIElement);
     },
 
     /**
      * Handle a keydown event.
      * @param {Event} e The keydown event.
-     * @return {boolean} Whether the key event was handled.
      */
     handleKeyDown: function(e) {
-      if (this.disabled)
-        return;
-
-      return this.selectionController_.handleKeyDown(e);
+      if (!this.disabled)
+        this.selectionController_.handleKeyDown(e);
     },
 
     /**
@@ -554,7 +553,7 @@
     /**
      * Callback from the selection model. We dispatch {@code change} events
      * when the selection changes.
-     * @param {!Event} e Event with change info.
+     * @param {!Event} ce Event with change info.
      * @private
      */
     handleOnChange_: function(ce) {
@@ -606,7 +605,7 @@
           var self = this;
           window.setTimeout(function() {
             self.scrollIndexIntoView(pe.newValue);
-          });
+          }, 0);
         }
       }
     },
@@ -797,7 +796,7 @@
 
     /**
      * Creates a new list item.
-     * @param {*} value The value to use for the item.
+     * @param {Object} value The value to use for the item.
      * @return {!ListItem} The newly created list item.
      */
     createItem: function(value) {
@@ -1062,7 +1061,7 @@
         this.firstIndex_ = 0;
         this.lastIndex_ = 0;
         this.remainingSpace_ = this.clientHeight != 0;
-        this.mergeItems(0, 0, {}, {});
+        this.mergeItems(0, 0);
         return;
       }
 
@@ -1276,10 +1275,11 @@
 
   /**
    * Mousedown event handler.
-   * @this {List}
-   * @param {MouseEvent} e The mouse event object.
+   * @this {cr.ui.List}
+   * @param {Event} e The mouse event object.
    */
   function handleMouseDown(e) {
+    e.target = /** @type {!HTMLElement} */(e.target);
     var listItem = this.getListItemAncestor(e.target);
     var wasSelected = listItem && listItem.selected;
     this.handlePointerDownUp_(e);
@@ -1307,10 +1307,11 @@
    * Dragstart event handler.
    * If there is an item at starting position of drag operation and the item
    * is not selected, select it.
-   * @this {List}
-   * @param {MouseEvent} e The event object for 'dragstart'.
+   * @this {cr.ui.List}
+   * @param {Event} e The event object for 'dragstart'.
    */
   function handleDragStart(e) {
+    e = /** @type {MouseEvent} */(e);
     var element = e.target.ownerDocument.elementFromPoint(e.clientX, e.clientY);
     var listItem = this.getListItemAncestor(element);
     if (!listItem)