vm_service: Make SocketProfile.sockets non-late.

We only need to adjust a private constructor to make it non-late
[1] [2].

[1]: https://dart.dev/effective-dart/usage#dont-use-late-when-a-constructor-initializer-list-will-do
[2]: https://dart.dev/effective-dart/design#avoid-public-late-final-fields-without-initializers

Change-Id: Ia063718104027a1cec147ca94d7ce34a661f5efd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/435000
Reviewed-by: Ben Konyi <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/vm_service/lib/src/dart_io_extensions.dart

@@ -270,18 +270,18 @@ class SocketProfile extends Response {
   String get type => 'SocketProfile';
 
   /// List of socket statistics.
-  late final List<SocketStatistic> sockets;
+  final List<SocketStatistic> sockets;
 
   SocketProfile({required this.sockets});
 
-  SocketProfile._fromJson(Map<String, dynamic> json) {
-    // TODO(bkonyi): make this part of the vm_service.dart library so we can
-    // call super._fromJson.
-    sockets = List<SocketStatistic>.from(
-        createServiceObject(json['sockets'], const ['SocketStatistic'])
-                as List? ??
-            []);
-  }
+  SocketProfile._fromJson(Map<String, dynamic> json)
+      :
+        // TODO(bkonyi): make this part of the vm_service.dart library so we can
+        // call super._fromJson.
+        sockets = List<SocketStatistic>.from(
+            createServiceObject(json['sockets'], const ['SocketStatistic'])
+                    as List? ??
+                []);
 }
 
 /// A [Response] containing the enabled state of a service extension.