Resynthesize invalid constants as unresolved identifiers.

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

Index: pkg/analyzer/lib/src/summary/resynthesize.dart
diff --git a/pkg/analyzer/lib/src/summary/resynthesize.dart b/pkg/analyzer/lib/src/summary/resynthesize.dart
index 53689173f3b7e1f453b4ffa0ad7acb329b5c715e..085136b6d95bd4041a3976cac80a744b476c025f 100644
--- a/pkg/analyzer/lib/src/summary/resynthesize.dart
+++ b/pkg/analyzer/lib/src/summary/resynthesize.dart
@@ -262,7 +262,9 @@ class _ConstExprBuilder {
   Expression get expr => stack.single;
 
   Expression build() {
-    // TODO(scheglov) complete implementation
+    if (uc.isInvalid) {
+      return AstFactory.identifier3(r'$$invalidConstExpr$$');
+    }
     for (UnlinkedConstOperation operation in uc.operations) {
       switch (operation) {
         case UnlinkedConstOperation.pushNull: