prefer const constructor (#8292)

packages/flutter_tools/lib/src/base/utils.dart

diff --git a/packages/flutter_tools/lib/src/base/utils.dart b/packages/flutter_tools/lib/src/base/utils.dart
index 7fe223b..608fa7e 100644
--- a/packages/flutter_tools/lib/src/base/utils.dart
+++ b/packages/flutter_tools/lib/src/base/utils.dart
@@ -73,7 +73,7 @@
 }
 
 String toPrettyJson(Object jsonable) {
-  return new JsonEncoder.withIndent('  ').convert(jsonable) + '\n';
+  return const JsonEncoder.withIndent('  ').convert(jsonable) + '\n';
 }
 
 /// Return a String - with units - for the size in MB of the given number of bytes.