[MD Extensions] Respond with a load error when loading unpacked fails

chrome/browser/extensions/api/developer_private/developer_private_api.h

Index: chrome/browser/extensions/api/developer_private/developer_private_api.h
diff --git a/chrome/browser/extensions/api/developer_private/developer_private_api.h b/chrome/browser/extensions/api/developer_private/developer_private_api.h
index 607e3029d07975be4212803d74caa8cfccea0998..8c9718ad8b87bd94727d4a70d1a8f1df725e737c 100644
--- a/chrome/browser/extensions/api/developer_private/developer_private_api.h
+++ b/chrome/browser/extensions/api/developer_private/developer_private_api.h
@@ -395,8 +395,17 @@ class DeveloperPrivateLoadUnpackedFunction
                       const std::string& error);
 
  private:
+  void OnGotManifestError(const base::FilePath& file_path,
+                          const std::string& error,
+                          size_t line_number,
+                          const std::string& manifest);
+
   // Whether or not we should fail quietly in the event of a load error.
-  bool fail_quietly_;
+  bool fail_quietly_ = false;
+
+  // Whether we populate a developer_private::LoadError on load failure, as
+  // opposed to simply passing the message in lastError.
+  bool populate_error_ = false;
 };
 
 class DeveloperPrivateChoosePathFunction