Complain about uninitialized const fields.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

 // Copyright (c) 2016, 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.
 
 library fasta.body_builder;
 
 import '../parser/parser.dart' show FormalParameterType, optional;
 
 import '../parser/error_kind.dart' show ErrorKind;
 
@@ skipping 960 matching lines @@
   @override
   void endFieldInitializer(Token assignmentOperator) {
     debugEvent("FieldInitializer");
     assert(assignmentOperator.stringValue == "=");
     push(popForValue());
   }
 
   @override
   void handleNoFieldInitializer(Token token) {
     debugEvent("NoFieldInitializer");
-    push(NullValue.FieldInitializer);
+    if (constantExpressionRequired) {
+      addCompileTimeError(
+          token.charOffset, "const field must have initializer.");
+      // Creating a null value to prevent the Dart VM from crashing.
+      push(new NullLiteral()..fileOffset = token.charOffset);
+    } else {
+      push(NullValue.FieldInitializer);
+    }
   }
 
   @override
   void endInitializedIdentifier(Token nameToken) {
     // TODO(ahe): Use [InitializedIdentifier] here?
     debugEvent("InitializedIdentifier");
     VariableDeclaration variable = pop();
     variable.fileOffset = nameToken.charOffset;
     push(variable);
     scope[variable.name] = new KernelVariableBuilder(
@@ skipping 1865 matching lines @@
   } else if (node is PrefixBuilder) {
     return node.name;
   } else if (node is ThisAccessor) {
     return node.isSuper ? "super" : "this";
   } else if (node is BuilderAccessor) {
     return node.plainNameForRead;
   } else {
     return internalError("Unhandled: ${node.runtimeType}");
   }
 }