Add a compile time error for non-static const fields

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 973 matching lines @@
   C() {
     return 1;
   }
 }
 
 main() => new C();"""]);
 
   static const MessageKind ILLEGAL_FINAL_METHOD_MODIFIER = const MessageKind(
       "Cannot have final modifier on method.");
 
+  static const MessageKind ILLEGAL_CONST_FIELD_MODIFIER = const MessageKind(
+      "Cannot have const modifier on non-static field.",
+      howToFix: "Try adding a static modifier, or removing the const modifier.",
+      examples: const ["""
+class C {
+  const int a = 1;
+}
+
+main() => new C();"""]);
+
   static const MessageKind ILLEGAL_CONSTRUCTOR_MODIFIERS = const MessageKind(
       "Illegal constructor modifiers: '#{modifiers}'.");
 
   static const MessageKind ILLEGAL_MIXIN_APPLICATION_MODIFIERS =
       const MessageKind(
           "Illegal mixin application modifiers: '#{modifiers}'.");
 
   static const MessageKind ILLEGAL_MIXIN_SUPERCLASS = const MessageKind(
       "Class used as mixin must have Object as superclass.");
 
@@ skipping 1109 matching lines @@
   static String convertToString(value) {
     if (value is ErrorToken) {
       // Shouldn't happen.
       return value.assertionMessage;
     } else if (value is Token) {
       value = value.value;
     }
     return '$value';
   }
 }