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

extensions/browser/extension_error.cc

Index: extensions/browser/extension_error.cc
diff --git a/extensions/browser/extension_error.cc b/extensions/browser/extension_error.cc
index d8733fe51dc0234222f57984b487615512137855..19a31ea9ed529a6fdce9da60559bd23a6a09f17e 100644
--- a/extensions/browser/extension_error.cc
+++ b/extensions/browser/extension_error.cc
@@ -158,6 +158,10 @@
 }
 
 scoped_ptr<DictionaryValue> RuntimeError::ToValue() const {
+  // The items which are to be written into value are also described in
+  // chrome/browser/resources/extensions/extension_error_overlay.js in @typedef
+  // for RuntimeError and StackTrace. Please update them whenever you add or
+  // remove any keys here.
   scoped_ptr<DictionaryValue> value = ExtensionError::ToValue();
   value->SetString(kContextUrlKey, context_url_.spec());
   value->SetInteger(kRenderViewIdKey, render_view_id_);