Add missing return types for function parameters in ui/

These are required for the upcoming TypeScript 3.9.2 upgrade.

[email protected]

Bug: 1011811
Change-Id: Ibb7000f4c70863549bf6ce160a9fb89cb163e6f7
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2199122
Commit-Queue: Jack Franklin <[email protected]>
Reviewed-by: Jack Franklin <[email protected]>
Auto-Submit: Tim van der Lippe <[email protected]>
diff --git a/front_end/ui/DropTarget.js b/front_end/ui/DropTarget.js
index e77da39..fe99e77 100644
--- a/front_end/ui/DropTarget.js
+++ b/front_end/ui/DropTarget.js
@@ -15,7 +15,7 @@
    * @param {!Element} element
    * @param {!Array<{kind: string, type: !RegExp}>} transferTypes
    * @param {string} messageText
-   * @param {function(!DataTransfer)} handleDrop
+   * @param {function(!DataTransfer):*} handleDrop
    */
   constructor(element, transferTypes, messageText, handleDrop) {
     element.addEventListener('dragenter', this._onDragEnter.bind(this), true);