Add a new Device backed by flutter_tester. (#16405)

packages/flutter_tools/lib/src/build_info.dart

diff --git a/packages/flutter_tools/lib/src/build_info.dart b/packages/flutter_tools/lib/src/build_info.dart
index f0ecb7e..82e7dea 100644
--- a/packages/flutter_tools/lib/src/build_info.dart
+++ b/packages/flutter_tools/lib/src/build_info.dart
@@ -157,6 +157,7 @@
   linux_x64,
   windows_x64,
   fuchsia,
+  tester,
 }
 
 String getNameForTargetPlatform(TargetPlatform platform) {
@@ -179,6 +180,8 @@
       return 'windows-x64';
     case TargetPlatform.fuchsia:
       return 'fuchsia';
+    case TargetPlatform.tester:
+      return 'flutter-tester';
   }
   assert(false);
   return null;