Complain about function literals not being constant expressions.

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 '../fasta_codes.dart'
     show FastaMessage, codeExpectedButGot, codeExpectedFunctionBody;
 
 import '../parser/parser.dart' show FormalParameterType, MemberKind, optional;
@@ skipping 2136 matching lines @@
     Statement body = popStatement();
     AsyncMarker asyncModifier = pop();
     exitLocalScope();
     FormalParameters formals = pop();
     exitFunction();
     List<TypeParameter> typeParameters = pop();
     FunctionNode function = formals.addToFunction(new FunctionNode(body,
         typeParameters: typeParameters, asyncMarker: asyncModifier)
       ..fileOffset = beginToken.charOffset
       ..fileEndOffset = token.charOffset);
-    push(astFactory.functionExpression(function, beginToken));
+    if (constantExpressionRequired) {
+      push(buildCompileTimeError(
+          "Not a constant expression.", formals.charOffset));
+    } else {
+      push(astFactory.functionExpression(function, beginToken));
+    }
   }
 
   @override
   void endDoWhileStatement(
       Token doKeyword, Token whileKeyword, Token endToken) {
     debugEvent("DoWhileStatement");
     Expression condition = popForValue();
     Statement body = popStatement();
     JumpTarget continueTarget = exitContinueTarget();
     JumpTarget breakTarget = exitBreakTarget();
@@ skipping 1020 matching lines @@
     if (starToken == null) {
       return AsyncMarker.Async;
     } else {
       assert(identical(starToken.stringValue, "*"));
       return AsyncMarker.AsyncStar;
     }
   } else {
     return internalError("Unknown async modifier: $asyncToken");
   }
 }