[Extensions] Make chrome://extensions use developerPrivate for unpacked loading

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 be0c25e5273047dd4abbe4743b69fae726df5178..cf95fc173ef04a1c3ce2345e026edda8ebd2388c 100644
--- a/chrome/browser/extensions/api/developer_private/developer_private_api.h
+++ b/chrome/browser/extensions/api/developer_private/developer_private_api.h
@@ -312,6 +312,7 @@ class DeveloperPrivateLoadUnpackedFunction
  public:
   DECLARE_EXTENSION_FUNCTION("developerPrivate.loadUnpacked",
                              DEVELOPERPRIVATE_LOADUNPACKED);
+  DeveloperPrivateLoadUnpackedFunction();
 
  protected:
   ~DeveloperPrivateLoadUnpackedFunction() override;
@@ -320,6 +321,15 @@ class DeveloperPrivateLoadUnpackedFunction
   // EntryPickerClient:
   void FileSelected(const base::FilePath& path) override;
   void FileSelectionCanceled() override;
+
+  // Callback for the UnpackedLoader.
+  void OnLoadComplete(const Extension* extension,
+                      const base::FilePath& file_path,
+                      const std::string& error);
+
+ private:
+  // Whether or not we should fail quietly in the event of a load error.
+  bool fail_quietly_;
 };
 
 class DeveloperPrivateChoosePathFunction