Non-fatal errors in compile-time constants.

dart/pkg/compiler/lib/src/constants/expressions.dart

Index: dart/pkg/compiler/lib/src/constants/expressions.dart
diff --git a/dart/pkg/compiler/lib/src/constants/expressions.dart b/dart/pkg/compiler/lib/src/constants/expressions.dart
index fe1357de51c8425d27e2e9c4a3141c263c3ddf08..ef416fac9ce86ef516bac949d816b61ebc1f5fc9 100644
--- a/dart/pkg/compiler/lib/src/constants/expressions.dart
+++ b/dart/pkg/compiler/lib/src/constants/expressions.dart
@@ -45,6 +45,17 @@ abstract class ConstantExpression {
   }
 }
 
+/// A synthetic constant used to recover from errors.
+class ErroneousConstantExpression extends ConstantExpression {
+  final PrimitiveConstantValue value = new NullConstantValue();
+
+  ErroneousConstantExpression();
+
+  accept(ConstantExpressionVisitor visitor, [context]) {
+    // Do nothing. This is an error.
+  }
+}
+
 /// Boolean, int, double, string, or null constant.
 class PrimitiveConstantExpression extends ConstantExpression {
   final PrimitiveConstantValue value;