Verify a corner case of const constructor cycle detection with summaires.

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

Index: pkg/analyzer/test/src/summary/linker_test.dart
diff --git a/pkg/analyzer/test/src/summary/linker_test.dart b/pkg/analyzer/test/src/summary/linker_test.dart
index 59edb00bd506dcd541fca62fb97f0e0007eb0e26..d7526aba95806367b99c7fdc098bfe3001b9feb3 100644
--- a/pkg/analyzer/test/src/summary/linker_test.dart
+++ b/pkg/analyzer/test/src/summary/linker_test.dart
@@ -109,6 +109,19 @@ class C extends B {
     // No assertions--just make sure it doesn't crash.
   }
 
+  void test_constCycle_viaLength() {
+    createLinker('''
+class C {
+  final y;
+  const C() : y = x.length;
+}
+const x = [const C()];
+''');
+    testLibrary.libraryCycleForLink.ensureLinked();
+    ClassElementForLink classC = testLibrary.getContainedName('C');
+    expect(classC.unnamedConstructor.isCycleFree, false);
+  }
+
   void test_inferredType_instanceField_dynamic() {
     createLinker('''
 var x;