When building summaries from ASTs, handle circularities involving .length.

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 a8dde28e7783bbb411871174cbc83362c16bb26c..e961d784e75eea54eda54797e2bd70a26a2e66e3 100644
--- a/pkg/analyzer/test/src/summary/summary_common.dart
+++ b/pkg/analyzer/test/src/summary/summary_common.dart
@@ -4179,6 +4179,21 @@ class C {
     checkConstCycle('C');
   }
 
+  test_constructorCycle_viaLength() {
+    // It's not valid Dart but we need to make sure it doesn't crash
+    // summary generation.
+    serializeLibraryText(
+        '''
+class C {
+  final x;
+  const C() : x = y.length;
+}
+const y = const C();
+''',
+        allowErrors: true);
+    checkConstCycle('C');
+  }
+
   test_constructorCycle_viaNamedConstructor() {
     serializeLibraryText('''
 class C {