[App Shell] Add dev tools for debugging

apps/shell/app/shell_main_delegate.cc

Index: apps/shell/app/shell_main_delegate.cc
diff --git a/apps/shell/app/shell_main_delegate.cc b/apps/shell/app/shell_main_delegate.cc
index 964c4c543f866ef5fbb5aa8671634e38f179357f..bd8e0cffc2eba4565aa8e6d3b0c91e6cf77f06d9 100644
--- a/apps/shell/app/shell_main_delegate.cc
+++ b/apps/shell/app/shell_main_delegate.cc
@@ -97,6 +97,13 @@ void ShellMainDelegate::InitializeResourceBundle() {
   PathService::Get(chrome::FILE_RESOURCES_PACK, &resources_pack_path);
   ResourceBundle::GetSharedInstance().AddDataPackFromPath(
       resources_pack_path, ui::SCALE_FACTOR_NONE);
+  // The dev tool needs shell_devtools_discovery_page.html from
+  // content_shell.pak file.
+  base::FilePath pak_file, pak_dir;
+  PathService::Get(base::DIR_MODULE, &pak_dir);
+  pak_file = pak_dir.Append(FILE_PATH_LITERAL("content_shell.pak"));
+  ResourceBundle::GetSharedInstance().AddDataPackFromPath(
+      pak_file, ui::SCALE_FACTOR_NONE);
 }
 
 }  // namespace apps