Complain about uninitialized const fields.

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

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index 99d52df96e4e934f17d9a0273722e96a9d053a75..98c470af7236bc1b971c18bdb0ed509822aeb2c2 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -978,7 +978,14 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
   @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