Constrain constant references from deferred libraries

sdk/lib/_internal/compiler/implementation/warnings.dart

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
diff --git a/sdk/lib/_internal/compiler/implementation/warnings.dart b/sdk/lib/_internal/compiler/implementation/warnings.dart
index a67dc21b274a89380d03f19bc7ebb1fce5200718..e1f4f33b141d9dd08bc6806d6af248e405ae8fa3 100644
--- a/sdk/lib/_internal/compiler/implementation/warnings.dart
+++ b/sdk/lib/_internal/compiler/implementation/warnings.dart
@@ -554,7 +554,11 @@ main() => new C<String>();
       "Not a compile-time constant.");
 
   static const MessageKind DEFERRED_COMPILE_TIME_CONSTANT = const MessageKind(
-      "Deferred classes cannot be used to create compile-time constants.");
+      "A Deferred value cannot be used as a compile-time constant.");
+
+  static const MessageKind DEFERRED_COMPILE_TIME_CONSTANT_CONSTRUCTION =
+      const MessageKind("A deferred class cannot be used to create a"
+          "compile-time constant.");
 
   static const MessageKind CYCLIC_COMPILE_TIME_CONSTANTS = const MessageKind(
       "Cycle in the compile-time constant computation.");