Remove @VisibleForTesting from FirebaseApp constructor (#1392)

* Remove @VisibleForTesting from FirebaseApp constructor

* Add todo for tracking apps

* fix tests

* Update packages/firebase_core/lib/src/firebase_app.dart

Co-Authored-By: Collin Jackson <[email protected]>

* Update packages/firebase_core/lib/src/firebase_app.dart

Co-Authored-By: Collin Jackson <[email protected]>

Author: kroikie

packages/firebase_core/lib/src/firebase_app.dart

@@ -5,8 +5,8 @@
 part of firebase_core;
 
 class FirebaseApp {
-  @visibleForTesting
-  const FirebaseApp({@required this.name}) : assert(name != null);
+  // TODO(jackson): We could assert here that an app with this name was configured previously.
+  FirebaseApp({@required this.name}) : assert(name != null);
 
   /// The name of this app.
   final String name;

packages/firebase_core/test/firebase_core_test.dart

@@ -11,7 +11,7 @@ void main() {
 
   group('$FirebaseApp', () {
     final List<MethodCall> log = <MethodCall>[];
-    const FirebaseApp testApp = FirebaseApp(
+    final FirebaseApp testApp = FirebaseApp(
       name: 'testApp',
     );
     const FirebaseOptions testOptions = FirebaseOptions(