Use the stack_trace library in scheduled_test.

pkg/stack_trace/lib/src/frame.dart

Index: pkg/stack_trace/lib/src/frame.dart
diff --git a/pkg/stack_trace/lib/src/frame.dart b/pkg/stack_trace/lib/src/frame.dart
index 5f0777c16188d990b16daae0bd4817187cfc8244..f05b4692809529cb5b4f4771176e581c176933c7 100644
--- a/pkg/stack_trace/lib/src/frame.dart
+++ b/pkg/stack_trace/lib/src/frame.dart
@@ -46,6 +46,13 @@ class Frame {
     return path.relative(fileUriToPath(uri));
   }
 
+  /// Returns the name of the package this stack frame comes from, or `null` if
+  /// this stack frame doesn't come from a `package:` URL.
+  String get package {
+    if (uri.scheme != 'package') return null;
+    return uri.path.split('/').first;
+  }
+
   /// A human-friendly description of the code location.
   ///
   /// For Dart core libraries, this will omit the line and column information,