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

chrome/browser/resources/extensions/pack_extension_overlay.js

Index: chrome/browser/resources/extensions/pack_extension_overlay.js
diff --git a/chrome/browser/resources/extensions/pack_extension_overlay.js b/chrome/browser/resources/extensions/pack_extension_overlay.js
index 22a316501525994545f0585d458331f709dd9408..186f84102e632463ca50099b89a95438d9c8c4b9 100644
--- a/chrome/browser/resources/extensions/pack_extension_overlay.js
+++ b/chrome/browser/resources/extensions/pack_extension_overlay.js
@@ -60,9 +60,9 @@
      * @private
      */
     showFileDialog_: function(selectType, operation, callback) {
-      handleFilePathSelected = function(filePath) {
+      window.handleFilePathSelected = function(filePath) {
         callback(filePath);
-        handleFilePathSelected = function() {};
+        window.handleFilePathSelected = function() {};
       };
 
       chrome.send('packExtensionSelectFilePath', [selectType, operation]);
@@ -104,14 +104,14 @@
         '',
         function() {
           extensions.ExtensionSettings.showOverlay(null);
-        },
-        null);
+        });
     extensions.ExtensionSettings.showOverlay($('alertOverlay'));
   };
 
   /**
    * Post an alert overlay showing |message|, and upon acknowledgement, close
    * the alert overlay and return to showing the PackExtensionOverlay.
+   * @param {string} message The error message.
    */
   PackExtensionOverlay.showError = function(message) {
     alertOverlay.setValues(
@@ -121,8 +121,7 @@
         '',
         function() {
           extensions.ExtensionSettings.showOverlay($('pack-extension-overlay'));
-        },
-        null);
+        });
     extensions.ExtensionSettings.showOverlay($('alertOverlay'));
   };