Make Stream abstract as it is in the actual SDK.

pkg/analyzer/test/generated/analysis_context_factory.dart

Index: pkg/analyzer/test/generated/analysis_context_factory.dart
diff --git a/pkg/analyzer/test/generated/analysis_context_factory.dart b/pkg/analyzer/test/generated/analysis_context_factory.dart
index ffbe34921c7fc8126b4de3debc0bb37271fd0a57..69469fe79208d90e07f86d33c609cdf93601b96c 100644
--- a/pkg/analyzer/test/generated/analysis_context_factory.dart
+++ b/pkg/analyzer/test/generated/analysis_context_factory.dart
@@ -238,6 +238,7 @@ class AnalysisContextFactory {
     // Stream
     ClassElementImpl streamElement =
         ElementFactory.classElement2("Stream", ["T"]);
+    streamElement.abstract = true;
     streamElement.constructors = <ConstructorElement>[
       ElementFactory.constructorElement2(streamElement, null)
     ];