Compile more targets in foreground/js/ui in gyp v2 (3)

ui/file_manager/externs/drag_target.js

+// Copyright 2017 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.
+
+/**
+ * @constructor

[fukino, 2017/03/24 08:40:10]

@interface

[oka, 2017/03/27 02:21:18]

Done.

[oka, 2017/03/27 02:21:18]

Done.

+ * @extends {cr.ui.List}

[fukino, 2017/03/24 08:40:10]

This interface does not have to extend cr.ui.List.
How about: FileTableList and FileGrid extend cr.ui.List and implements
DragTarget.

[oka, 2017/03/27 02:21:18]

Removed @extends, and added type cast to callers of getHitElements.

Actually FileTableList is not the type of the variable what having
getHitElements, but cr.ui.List is. file_table.js adds the method to cr.ui.List.
So adding @implements would not be feasible.

+ */
+var DragTarget = function() {};
+
+/**
+ * This definition is required to satisfy
+ * ui/file_manager/file_manager/foreground/js/ui/drag_selector.js.
+ *
+ * @param {number} x
+ * @param {number} y
+ * @param {number=} opt_width
+ * @param {number=} opt_height
+ * @return {Array<number>}
+ */
+DragTarget.prototype.getHitElements = function(x, y, opt_width, opt_height) {};