Add spec for DevLoadingView (#24930)

Summary:
Part of #24875

## Changelog

[General] [Added] - add TM spec for DevLoadingView
Pull Request resolved: https://github.com/facebook/react-native/pull/24930

Reviewed By: RSNara

Differential Revision: D15423524

Pulled By: fkgozali

fbshipit-source-id: 18ca65abcd4fb3c0ec0434ccba0c0e1d97c17995

Libraries/Utilities/HMRLoadingView.ios.js

@@ -11,19 +11,23 @@
 'use strict';
 
 const processColor = require('../StyleSheet/processColor');
-const {DevLoadingView} = require('../BatchedBridge/NativeModules');
+import NativeDevLoadingView from './NativeDevLoadingView';
 
 class HMRLoadingView {
   static showMessage(message: string) {
-    DevLoadingView.showMessage(
-      message,
-      processColor('#000000'),
-      processColor('#aaaaaa'),
-    );
+    if (NativeDevLoadingView != null) {
+      NativeDevLoadingView.showMessage(
+        message,
+        processColor('#000000'),
+        processColor('#aaaaaa'),
+      );
+    }
   }
 
   static hide() {
-    DevLoadingView.hide();
+    if (NativeDevLoadingView != null) {
+      NativeDevLoadingView.hide();
+    }
   }
 }
 

Libraries/Utilities/NativeDevLoadingView.js

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+import type {TurboModule} from 'RCTExport';
+import * as TurboModuleRegistry from 'TurboModuleRegistry';
+
+export interface Spec extends TurboModule {
+  +showMessage: (
+    message: string,
+    color: Object,
+    backgroundColor: Object,
+  ) => void;
+  +hide: () => void;
+}
+
+export default TurboModuleRegistry.get<Spec>('DevLoadingView');