Typecheck some of ui/webui/resources/js/ with Closure compiler.

chrome/browser/resources/extensions/extension_error_overlay.js

Index: chrome/browser/resources/extensions/extension_error_overlay.js
diff --git a/chrome/browser/resources/extensions/extension_error_overlay.js b/chrome/browser/resources/extensions/extension_error_overlay.js
index afdcf56d2e64354e7a7ec2d41800ed06c5a3b9d9..537b6892b55bb24eeae734063ce2dd8c0d0cabd8 100644
--- a/chrome/browser/resources/extensions/extension_error_overlay.js
+++ b/chrome/browser/resources/extensions/extension_error_overlay.js
@@ -77,7 +77,7 @@ cr.define('extensions', function() {
     else if (chrome.developerPrivate)
       chrome.developerPrivate.openDevTools(args);
     else
-      assert(false, 'Cannot call either openDevTools function.');
+      assertNotReached('Cannot call either openDevTools function.');
   };
 
   RuntimeErrorContent.prototype = {
@@ -335,7 +335,7 @@ cr.define('extensions', function() {
         extensions.ExtensionErrorOverlay.requestFileSourceResponse(result);
       });
     } else {
-      assert(false, 'Cannot call either requestFileSource function.');
+      assertNotReached('Cannot call either requestFileSource function.');
     }
   };