[Flow] src/utils/DevtoolsUtils.js - add type defs for flow coverage (#5872)

Author: atwalg2

src/utils/DevToolsUtils.js

@@ -2,14 +2,16 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
 
+// @flow
+
 import assert from "./assert";
 
-export function reportException(who, exception) {
+export function reportException(who: string, exception: any[]) {
   const msg = `${who} threw an exception: `;
   console.error(msg, exception);
 }
 
-export function executeSoon(fn) {
+export function executeSoon(fn: Function) {
   setTimeout(fn, 0);
 }