Implement line and column numbers.

pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart

Index: pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart b/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart
index 019fb4c0fdd9625b03bb46a5b5397f8a4685770a..6e1e93c31c7f1b3aa4256214d21d238287fffbe5 100644
--- a/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart
@@ -10,6 +10,9 @@ import 'builder.dart' show
     Builder,
     TypeBuilder;
 
+import '../messages.dart' show
+    warning;
+
 import 'scope.dart' show
     Scope;
 
@@ -54,7 +57,7 @@ class ConstructorReferenceBuilder extends Builder {
       target = builder.constructors[suffix ?? ""];
     }
     if (target == null) {
-      print("Couldn't find constructor $fullNameForErrors.");
+      warning(null, -1, "Couldn't find constructor '$fullNameForErrors'.");
     }
   }
 }