Enable most of the constant AST serialization for AST-based summaries.

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

Index: pkg/analyzer/lib/src/summary/summarize_elements.dart
diff --git a/pkg/analyzer/lib/src/summary/summarize_elements.dart b/pkg/analyzer/lib/src/summary/summarize_elements.dart
index 1ac008ab64172a00b41b75fa1b913a3c35562feb..038c385709e2fea40732a26b9488d201f95d8f8a 100644
--- a/pkg/analyzer/lib/src/summary/summarize_elements.dart
+++ b/pkg/analyzer/lib/src/summary/summarize_elements.dart
@@ -65,7 +65,6 @@ class _ConstExprSerializer extends AbstractConstExprSerializer {
     Element element = identifier.staticElement;
     assert(element != null);
     // TODO(scheglov) how to serialize element references?
-    operations.add(UnlinkedConstOperation.pushReference);
     return new UnlinkedTypeRefBuilder(
         reference: serializer._getElementReferenceId(element));
   }