Fix summary handling of invalid annotations of the form `@a.b.c`.

pkg/analyzer/lib/src/summary/summarize_ast.dart

Index: pkg/analyzer/lib/src/summary/summarize_ast.dart
diff --git a/pkg/analyzer/lib/src/summary/summarize_ast.dart b/pkg/analyzer/lib/src/summary/summarize_ast.dart
index 6d885ef5021fca01fbb22d0629969c624234d084..ed52f79e1e931192b1351e3bc6c0c734a5f6e686 100644
--- a/pkg/analyzer/lib/src/summary/summarize_ast.dart
+++ b/pkg/analyzer/lib/src/summary/summarize_ast.dart
@@ -53,19 +53,19 @@ class _ConstExprSerializer extends AbstractConstExprSerializer {
 
   @override
   void serializeAnnotation(Annotation annotation) {
+    Identifier name = annotation.name;
+    EntityRefBuilder constructor;
+    if (name is PrefixedIdentifier && annotation.constructorName == null) {
+      constructor =
+          serializeConstructorRef(null, name.prefix, null, name.identifier);
+    } else {
+      constructor = serializeConstructorRef(
+          null, annotation.name, null, annotation.constructorName);
+    }
     if (annotation.arguments == null) {
-      assert(annotation.constructorName == null);
-      serialize(annotation.name);
+      references.add(constructor);
+      operations.add(UnlinkedExprOperation.pushReference);
     } else {
-      Identifier name = annotation.name;
-      EntityRefBuilder constructor;
-      if (name is PrefixedIdentifier && annotation.constructorName == null) {
-        constructor =
-            serializeConstructorRef(null, name.prefix, null, name.identifier);
-      } else {
-        constructor = serializeConstructorRef(
-            null, annotation.name, null, annotation.constructorName);
-      }
       serializeInstanceCreation(constructor, annotation.arguments);
     }
   }