Report an error if a const constructor calls a non-const constructor.

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

Index: sdk/lib/_internal/compiler/implementation/warnings.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/warnings.dart	(revision 25201)
+++ sdk/lib/_internal/compiler/implementation/warnings.dart	(working copy)
@@ -120,6 +120,8 @@
       "super call arguments and constructor parameters don't match");
   static const NO_MATCHING_CONSTRUCTOR_FOR_IMPLICIT = const MessageKind(
       "implicit super call arguments and constructor parameters don't match");
+  static const CONST_CALLS_NON_CONST = const MessageKind(
+      "const constructor cannot call a non-const constructor");
   static const INITIALIZING_FORMAL_NOT_ALLOWED = const MessageKind(
       'an initializing formal parameter is only allowed in '
       'non-redirecting generative constructors');