Report compile-time error if using `this` implicitly in initializers

pkg/compiler/lib/src/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 = "Computer says no!";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 137 matching lines @@
 
   static const MessageKind THIS_IS_THE_DECLARATION = const MessageKind(
       "This is the declaration of '#{name}'.");
 
   static const MessageKind THIS_IS_THE_METHOD = const MessageKind(
       "This is the method declaration.");
 
   static const MessageKind CANNOT_RESOLVE = const MessageKind(
       "Cannot resolve '#{name}'.");
 
+  static const MessageKind CANNOT_RESOLVE_IN_INITIALIZER = const MessageKind(
+      "Cannot resolve '#{name}'. It would be implicitly looked up on this "
+      "instance, but instances are not available in initializers.",
+      howToFix: "Try correcting the unresolved reference or move the "
+          "initialization to a constructor body.",
+      examples: const ["""
+class A {
+  var test = unresolvedName;
+}
+main() => new A();
+"""]);
+
   static const MessageKind CANNOT_RESOLVE_CONSTRUCTOR = const MessageKind(
       "Cannot resolve constructor '#{constructorName}'.");
 
   static const MessageKind CANNOT_RESOLVE_CONSTRUCTOR_FOR_IMPLICIT =
       const MessageKind("cannot resolve constructor '#{constructorName}'"
           " for implicit super call.",
       howToFix: "Try explicitly invoking a constructor of the super class",
       examples: const ["""
 class A {
   A.foo() {}
@@ skipping 2319 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';
   }
 }