Emit a compile-time error on const constructors with a body.

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

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 223 matching lines @@
   static const MessageKind INVALID_INITIALIZER = const MessageKind(
       'Error: Invalid initializer.');
 
   static const MessageKind FUNCTION_WITH_INITIALIZER = const MessageKind(
       'Error: Only constructors can have initializers.');
 
   static const MessageKind REDIRECTING_CONSTRUCTOR_CYCLE = const MessageKind(
       'Error: Cyclic constructor redirection.');
 
   static const MessageKind REDIRECTING_CONSTRUCTOR_HAS_BODY = const MessageKind(
-      'Error: Redirecting constructor cannot have a body.');
+      "Error: Redirecting constructor can't have a body.");
+
+  static const MessageKind CONST_CONSTRUCTOR_HAS_BODY = const MessageKind(
+      "Error: Const constructor or factory can't have a body.",
+      howToFix: "Remove the 'const' keyword or the body",
+      examples: const ["""
+class C {
+  const C() {}
+}
+
+main() => new C();"""]);
 
   static const MessageKind REDIRECTING_CONSTRUCTOR_HAS_INITIALIZER =
       const MessageKind(
           'Error: Redirecting constructor cannot have other initializers.');
 
   static const MessageKind SUPER_INITIALIZER_IN_OBJECT = const MessageKind(
       'Error: "Object" cannot have a super initializer.');
 
   static const MessageKind DUPLICATE_SUPER_INITIALIZER = const MessageKind(
       'Error: Cannot have more than one super initializer.');
@@ skipping 239 matching lines @@
   static const MessageKind OPERATOR_OPTIONAL_PARAMETERS = const MessageKind(
       'Error: Operator "#{operatorName}" cannot have optional parameters.');
 
   static const MessageKind OPERATOR_NAMED_PARAMETERS = const MessageKind(
       'Error: Operator "#{operatorName}" cannot have named parameters.');
 
   static const MessageKind CONSTRUCTOR_WITH_RETURN_TYPE = const MessageKind(
       'Error: Cannot have return type for constructor.');
 
   static const MessageKind CANNOT_RETURN_FROM_CONSTRUCTOR = const MessageKind(
-      "Error: Cannot return a value from a constructor.",
+      "Error: Constructors can't return values.",
       howToFix: "Remove the return statement or use a factory constructor.",
       examples: const ["""
 class C {
   C() {
     return 1;
   }
 }
 
 main() => new C();"""]);
 
@@ skipping 522 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, Map arguments, bool terse)
     : super(kind, arguments, terse);
 }