Clean up trivial cycle detection logic.

pkg/analyzer/test/src/summary/summary_common.dart

Index: pkg/analyzer/test/src/summary/summary_common.dart
diff --git a/pkg/analyzer/test/src/summary/summary_common.dart b/pkg/analyzer/test/src/summary/summary_common.dart
index e961d784e75eea54eda54797e2bd70a26a2e66e3..c690ab83d24bd3b7c7df332bfe7c2ee8d40045dc 100644
--- a/pkg/analyzer/test/src/summary/summary_common.dart
+++ b/pkg/analyzer/test/src/summary/summary_common.dart
@@ -4148,6 +4148,17 @@ class C {
     checkConstCycle('C', hasCycle: false);
   }
 
+  test_constructorCycle_trivial() {
+    serializeLibraryText(
+        '''
+class C {
+  const C() : this();
+}
+''',
+        allowErrors: true);
+    checkConstCycle('C');
+  }
+
   test_constructorCycle_viaFactoryRedirect() {
     serializeLibraryText(
         '''