Produce error when duplicate field initializers are found

tests/language/constructor_duplicate_initializers_test.dart

Index: tests/language/constructor_duplicate_initializers_test.dart
diff --git a/tests/language/constructor_duplicate_initializers_test.dart b/tests/language/constructor_duplicate_initializers_test.dart
index ab9a0994fcd091d91787278deb5986d6f531d036..5ba6d28a7ec0c2155dc43144888fec74474835a1 100644
--- a/tests/language/constructor_duplicate_initializers_test.dart
+++ b/tests/language/constructor_duplicate_initializers_test.dart
@@ -15,10 +15,13 @@ class Class {
       // formals and initializer list.
     : field_ = 2  /// 02: compile-time error
   ;
+  // Test against duplicate final field initialization in initializing formals.
+  Class.two_fields(this.field_, this.field_); /// 03: compile-time error

[ahe, 2012/08/16 11:56:43]

The test is more precise if you write it like this:

  Class.two_fields(this.field_
                  // Test against duplicate final field initialization
                  // in initializing formals.
                  , this.field_ /// 03: compile-time error
                  );

The advantage is that it reduces the chance that there is something else wrong
on the line and we end up not testing what we think we're testing.

   final field_;
 }
 
 main() {
   new Class(42);
   new Class.field(42);
+  new Class.two_fields(42, 42); /// 03: continued

[ahe, 2012/08/16 11:56:43]

Then this would also need rewriting.

 }