[Fabric] call setIsFabric(true) in the MainActivity

android/app/src/main/java/com/rnnewarchitectureapp/MainActivity.java

@@ -1,6 +1,8 @@
 package com.rnnewarchitectureapp;
 
 import com.facebook.react.ReactActivity;
+import com.facebook.react.ReactActivityDelegate;
+import com.facebook.react.ReactRootView;
 
 public class MainActivity extends ReactActivity {
 
@@ -12,4 +14,25 @@ public class MainActivity extends ReactActivity {
   protected String getMainComponentName() {
     return "RNNewArchitectureApp";
   }
+
+  // Add the Activity Delegate, if you don't have one already.
+  public static class MainActivityDelegate extends ReactActivityDelegate {
+
+    public MainActivityDelegate(ReactActivity activity, String mainComponentName) {
+      super(activity, mainComponentName);
+    }
+
+    @Override
+    protected ReactRootView createRootView() {
+      ReactRootView reactRootView = new ReactRootView(getContext());
+      reactRootView.setIsFabric(true);
+      return reactRootView;
+    }
+  }
+
+  // Make sure to override the `createReactActivityDelegate()` method.
+  @Override
+  protected ReactActivityDelegate createReactActivityDelegate() {
+    return new MainActivityDelegate(this, getMainComponentName());
+  }
 }