format initializer list of constructors (#27111)

packages/flutter_tools/lib/src/artifacts.dart

diff --git a/packages/flutter_tools/lib/src/artifacts.dart b/packages/flutter_tools/lib/src/artifacts.dart
index 371a042..6cfb8bc 100644
--- a/packages/flutter_tools/lib/src/artifacts.dart
+++ b/packages/flutter_tools/lib/src/artifacts.dart
@@ -76,9 +76,11 @@
 }
 
 class EngineBuildPaths {
-  const EngineBuildPaths({ @required this.targetEngine, @required this.hostEngine }):
-      assert(targetEngine != null),
-      assert(hostEngine != null);
+  const EngineBuildPaths({
+    @required this.targetEngine,
+    @required this.hostEngine,
+  }) : assert(targetEngine != null),
+       assert(hostEngine != null);
 
   final String targetEngine;
   final String hostEngine;